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PubMed2005

Pediatric powered wheelchairs: results of a national survey of providers.

A national survey of providers of pediatric powered wheelchairs was conducted to collect background data on these professionals and to develop a "model" of their current assessment and recommendation practices. Data collected in the survey included provider demographics, frequency of powered wheelchair provision to young children, common reasons for not recommending a powered wheelchair, reasons why a child who is recommended a powered wheelchair does not receive one, current pediatric powered wheelchair assessment and recommendation practices, and subjective data regarding the efficacy of these practices and the impact of powered wheelchairs on children. Respondents rated the frequency with which they performed various wheelchair assessment and recommendation practices, and these ratings were analyzed to determine activities that were performed frequently. These activities were then combined into common "factors" using factor analysis, and the results of the factor analysis were used to create a model of current pediatric powered wheelchair assessment and recommendation practices. A total of 140 surveys were received from providers in 46 states. Of these providers, 54% were clinicians (e.g., physical therapists, occupational therapists), and 46% were suppliers (e.g., Rehabilitation Technology Specialists), representing a variety of geographic locations and facility types. The 3 major reasons for not recommending a powered wheelchair included cognitive, physical, and behavioral factors. The 3 major reasons why a child who is recommended a powered wheelchair does not receive one included funding issues, lack of family support, and transportation issues. The model of current pediatric powered wheelchair provision includes 4 assessment factors: Preliminary Clinical Assessment, Intake, Advanced Clinical Assessment, and Consideration of Other Factors. Typical recommendations include both therapeutic and nonclinical interventions. A modified version of this model, which addresses some issues identified in the survey that limit wheelchair recommendations, is currently being tested at 4 clinical sites.

Adolescent↗

PubMed2002

Haplotype block structure and its applications to association studies: power and study designs.

Recent studies have shown that the human genome has a haplotype block structure, such that it can be divided into discrete blocks of limited haplotype diversity. In each block, a small fraction of single-nucleotide polymorphisms (SNPs), referred to as "tag SNPs," can be used to distinguish a large fraction of the haplotypes. These tag SNPs can potentially be extremely useful for association studies, in that it may not be necessary to genotype all SNPs; however, this depends on how much power is lost. Here we develop a simulation study to quantitatively assess the power loss for a variety of study designs, including case-control designs and case-parental control designs. First, a number of data sets containing case-parental or case-control samples are generated on the basis of a disease model. Second, a small fraction of case and control individuals in each data set are genotyped at all the loci, and a dynamic programming algorithm is used to determine the haplotype blocks and the tag SNPs based on the genotypes of the sampled individuals. Third, the statistical power of tests was evaluated on the basis of three kinds of data: (1) all of the SNPs and the corresponding haplotypes, (2) the tag SNPs and the corresponding haplotypes, and (3) the same number of randomly chosen SNPs as the number of tag SNPs and the corresponding haplotypes. We study the power of different association tests with a variety of disease models and block-partitioning criteria. Our study indicates that the genotyping efforts can be significantly reduced by the tag SNPs, without much loss of power. Depending on the specific haplotype block-partitioning algorithm and the disease model, when the identified tag SNPs are only 25% of all the SNPs, the power is reduced by only 4%, on average, compared with a power loss of approximately 12% when the same number of randomly chosen SNPs is used in a two-locus haplotype analysis. When the identified tag SNPs are approximately 14% of all the SNPs, the power is reduced by approximately 9%, compared with a power loss of approximately 21% when the same number of randomly chosen SNPs is used in a two-locus haplotype analysis. Our study also indicates that haplotype-based analysis can be much more powerful than marker-by-marker analysis.

Algorithms↗

PubMed2004

Power for genetic association studies with random allele frequencies and genotype distributions.

One of the first and most important steps in planning a genetic association study is the accurate estimation of the statistical power under a proposed study design and sample size. In association studies for candidate genes or in fine-mapping applications, allele and genotype frequencies are often assumed to be known when, in fact, they are unknown (i.e., random variables from some distribution). For example, if we consider a diallelic marker with allele frequencies of 0.5 and 0.5 and Hardy-Weinberg proportions, the three genotype frequencies are often assumed to be 0.25, 0.50, and 0.25, and the statistical power is calculated. Unfortunately, ignoring this source of variation can inflate the estimated power of the study. In the present article, we propose averaging the estimates of power over the distribution of the genotype frequencies to calculate the true estimate of power for a fixed allele frequency. For the usual situation, in which allele frequencies in a population are not known, we propose placing a prior distribution on the allele frequency, taking advantage of any available genotype information. This Bayesian approach provides a more accurate estimate of power. We present examples for quantitative and qualitative traits in cohort studies of unrelated individuals and results from an extensive series of examples that show that ignoring the uncertainty in allele frequencies can inflate the estimated power of the study. We also present the results from case-control studies and show that standard methods may also overestimate power. As discussed in this article, the approach of fixing allele frequencies even if they are not known is the common approach to power calculations. We show that ignoring the sources of variation in allele frequencies tends to result in overestimates of power and, consequently, in studies that are underpowered. Software in C is available at http://www.ambrosius.net/Power/.

Alleles↗

PubMed2002

Explosive power and asymmetry in leg muscle function in frequent fallers and non-fallers aged over 65.

BACKGROUND: although low strength is a risk factor for falls, lower limb explosive power is more predictive of functional difficulties than strength. Power may be more predictive of a future fall than strength per se. OBJECTIVE: to compare leg muscle strength and explosive power and asymmetry of leg strength and power of women aged 65 or over living at home, with and without a history of falls. DESIGN: a case controlled study of self-reported 'fallers' versus 'non-fallers'. SUBJECTS: twenty women, aged 65 or over, with a history of at least three falls in the previous year were age matched with 15 women with no history of falls in the previous year. METHODS: lower limb explosive power, isometric strength of the quadriceps and hamstrings, isokinetic concentric strength (100 degrees/sec) of the quadriceps, hamstrings, ankle plantar- and dorsi-flexors and quadriceps eccentric strength (100 degrees/sec). Habitual physical activity was assessed using the self-completed Habitual Activity Profile Questionnaire. RESULTS: the women with a history of falls were less active but were not significantly weaker in any of the strength measurements, apart from ankle dorsiflexion adjusted for body weight. Both groups had significant asymmetry in all the leg muscles for both strength and power. Although both groups were asymmetrical in their lower limb power, the fallers demonstrated a significantly greater asymmetry. When the least powerful legs were compared, the women with a history of falls were 24% less powerful for their weight than those who did not fall (P=0.04). CONCLUSIONS: weakness and asymmetry is prevalent in women aged 65 and over, with and without a history of falls. Poor lower limb explosive power combined with asymmetry between limbs may be more predictive of future falls than more traditional measurements of strength in older women who live independently.

Accidental Falls↗

PubMed1991

Effects of vasoactive drugs upon haemodynamic power and input impedance in normal rats.

STUDY OBJECTIVE: The objectives were (a) to describe the effects of vasoactive drugs in normal rats upon cardiovascular function assessed by computing aortic haemodynamic power and input impedance, each separated into their component parts, and (b) to study the relationship between left ventricular pulsatile power output and the vascular impedance. DESIGN: Haemodynamic power and input impedance were computed from measurements of aortic blood pressure and flow in normal rats. The rats were then given an infusion of a vasoconstrictor drug (methoxamine) followed by a vasodilator drug (hydralazine) in order to study the effects of changes in vascular impedance upon haemodynamic power. EXPERIMENTAL MATERIAL: The measurements were made on pentobarbitone anaesthetised male Wistar rats of approximately 400 g body weight (10 infused with Hartmann's solution as controls and 10 infused with the drugs). MEASUREMENTS AND MAIN RESULTS: Aortic total haemodynamic power was between 9.96 mW and 10.37 mW during the control period and reached a maximum of 11.36 mW during the methoxamine infusion, but this difference was not statistically significant. It then decreased significantly to 4.32 mW by the end of the hydralazine infusion. Pulsatile power was only 0.32(SEM 0.08) mW (2.8% of the total power) in the control state and decreased to 0.12(0.1) mW (1.7%) during the methoxamine infusion, but increased to 0.59(0.15) mW (12.5%) by the end of the hydralazine infusion. The vascular effects were complex and involved all four of the input impedance parameters--peripheral resistance, characteristic resistance, arterial compliance, and inertance. Reflex responses of the vascular wall were apparent as temporal changes in characteristic resistance and arterial compliance. CONCLUSIONS: Changes in cardiovascular function can be described by computing haemodynamic power and input impedance and then separating these into their component parts. Administration of the vasoactive drugs affected left ventricular mean and pulsatile power output and all four components of the input impedance. The frequency distribution of left ventricular pulsatile power output may be matched to the vascular impedance in order to optimise tissue perfusion.

Animals↗

PubMed1997

Leg extension power and walking speed in very old people living independently.

BACKGROUND: Leg extension power can be determined as the product of the force and velocity of movement. Its association with maximal walking speed was studied in 131 80- and 85-year-old men and women. METHODS: Leg extension power was measured with the help of a sledge ergometer in a sitting position using a facilitated "jump test." The participant was attached by belts to a sliding chair on rails inclined at 12.6 degrees to the floor. The feet were placed on the force plate attached perpendicularly to the rails, and the knee angle was 90 degrees at the starting position. The participant was advised to extend his or her legs powerfully. The highest value of five to eight attempts was accepted as the result. The results were adjusted for body mass and expressed as watts.kilogram-1. Maximal walking speed was measured in the laboratory corridor over a distance of 10 m. RESULTS: Men and 80-year-old subjects exhibited greater leg extension power and were faster walkers than women and 85-year-old persons. Leg extension power correlated positively with maximal walking speed in all groups: the correlation coefficients were .412 in the 80-year-old men (n = 41, p = .007), .619 in the 80-year-old women (n = 56, p < .001), .939 in the 85-year-old men (n = 8, p = .001), and.685 in the 85-year-old women (n = 23, p < .001). The regression lines for leg extension power and walking speed were coincident, indicating that the power requirements to attain a given walking speed were similar for both sexes. The minimum power threshold for those with a maximal walking speed of 1.30-1.49 m.s-1 was on the order of 4 W.kg-1; a maximal walking speed of 1.50-1.99 m.s-1 required 7 W.kg-1; and for a speed over 2.00 m.s-1 the power threshold was 9.5 W.kg-1. CONCLUSIONS: Their lower average leg extension power may be one of the factors explaining the greater prevalence of mobility problems among women than men.

Activities of Daily Living↗

PubMed1999

Changes in power with resistance training in older and younger men and women.

BACKGROUND: Muscle power diminishes with increasing age and inactivity. The capacity for older adults to increase muscle power with resistance exercise has not been examined; therefore, we examined the influence of progressive resistance training (PRT) on muscle power output in 17 men and women aged 56-66 years, and compared their responses to 15 men and women aged 21-30 years. METHODS: All subjects performed 12 weeks of PRT at a workload equivalent to 80% of the one repetition maximum (1RM). All training and assessments of 1RM and power were made on Keiser pneumatic resistance machines. Subjects performed five exercises, three sets per exercise, twice weekly. Muscle power was measured (isotonically) at resistances equivalent to 40, 60, and 80% of the 1RM, on the knee extension and arm pull machines. RESULTS: All subjects increased arm pull power similarly at 40 and 60% of 1RM, independent of age or sex. There was not a significant increase in arm pull power at 80% of 1RM. Older and younger subjects also had similar absolute increases in leg extensor power at 40 and 60% of 1RM, but men responded with greater absolute gains than women at these percentages (p < .05). The increase in leg extensor power at 80% of 1RM was similar in all groups. Older and younger subjects increased strength similarly in all exercises except the left knee extension. Independent of age, men increased strength more than women in all exercises except the double leg press. CONCLUSIONS: These data demonstrate that individuals in their sixth decade can still improve muscle power (and strength); however, men may realize greater absolute gains than women.

Adult↗

PubMed2005

Upper and lower limb muscle power relationships in mobility-limited older adults.

BACKGROUND: Lower limb muscle power impairments are modifiable factors underlying mobility limitations in older adults. This study examined relationships between upper and lower limb muscle power and their role in predicting mobility performance among community-dwelling older adults. METHODS: A cross-sectional analysis was conducted. Participants included 37 mobility-limited adults (24 women, 13 men), aged 65 to 93 years. Measures included upper (elbow extension) and lower limb (double leg press) one repetition maximum (1RM), and muscle power at both 40% and 70% one repetition maximum. Physical performance measures included stair climb time, the Short Physical Performance Battery, and 4-meter walk time. Factors commonly mediating the relationship between impairments and physical performance were analyzed as covariates. RESULTS: Participants had a mean age of 76 years, had five chronic medical conditions, and manifested moderate mobility limitations. Although the associations between the upper and lower limbs were strong (p <.001), the magnitude of association was greater for power (r =.88-.89) as compared to strength (r =.69). Multivariate regression analyses revealed consistently strong relationships between limb muscle power and mobility performance measures. Substituting upper for lower limb power within these models did not materially weaken the relationships. CONCLUSION: Muscle power appears to be a more generalized attribute between the upper and lower limbs than is muscle strength, suggesting that mechanisms underlying velocity of movement, as opposed to force production, may be important factors underlying muscle power in elderly persons. Additionally, upper limb muscle power measures may serve as a useful surrogate measure of limb power having implications for clinicians and researchers.

Aged↗

PubMed2006

Power training improves balance in healthy older adults.

BACKGROUND: Age-related decline in muscle power may be an early indicator of balance deficits and fall risk, even in nonfrail adults. This study examined the dose-dependent effect of power training on balance performance in healthy older adults. METHODS: One hundred twelve community-dwelling healthy older adults (69 +/- 6 years) were randomized to 8-12 weeks of power training at 20% (LOW), 50% (MED), or 80% (HIGH) of maximal strength, or a nontraining control (CON) group. Participants trained twice weekly (five exercises; three sets of eight rapid concentric/slow eccentric repetitions) using pneumatic resistance machines. Balance, muscle performance (strength, power, endurance, contraction velocity), and body composition were measured. RESULTS: Power training significantly improved balance performance (p =.006) in participants who underwent power training compared to controls. Low intensity power training produced the greatest improvement in balance performance (p =.048). Average contraction velocity at low load (40% one repetition maximum [1RM]) at baseline independently predicted improvement in balance following training (r = -.29, p =.004). CONCLUSIONS: Power training improves balance, particularly using a low load, high velocity regimen, in older adults with initial lower muscle power and slower contraction. Further studies are warranted to define the mechanisms underlying this adaptation, as well as the optimum power training intensity for a range of physiological and clinical outcomes in older adults with varying levels of health status and functional independence.

Aged↗

PubMed1982

Effect of increased radiant warmer power output on state of hydration in the critically ill neonate.

To correlate radiant warmer bed power output with state of hydration in the critically ill infant, warmer power input was measured by a wattmeter and recorded by an on-line computer every 5 sec for 2 periods of 8-24 h each in 11 newborns with respiratory distress syndrome (mean birth weight 1.42 kg, mean gestational age 31.4 weeks). The 2 periods were compared to define a high and a low radiant power period. Fluid intake and urine output, urine and serum osmolalities, serum electrolytes, and free water clearance during each study period (high vs low radiant power) were also compared. Mean radiant power density received during periods of high radiant power output (8.93 mw/cm2) was significantly greater than during periods of low radiant power output (7.85 mw/cm2, p less than 0.001). Mean urine osmolality and fluid intake to output ratio were also significantly increased during periods of high radiant power density. There was a trend toward increased serum osmolality and decreased free water clearance during periods of high radiant power; however, these differences were not significant. This study suggests that prospective measurement of radiant power density delivered to critically ill newborns may be clinically significant in predicting an infant's state of hydration.

Critical Care↗

PubMed2000

Comparison of harmonic and conventional power Doppler ultrasonography for assessment of slow flow in hyperechoic tissue: experimental study using a Doppler phantom.

RATIONALE AND OBJECTIVES: Despite the advantages of depicting slow flow in small vessels, conventional power Doppler ultrasound (US) has a basic limitation, specifically that artifactual power Doppler signals mimic blood flow, especially in hyperechoic tissue. The purpose of this study was to compare harmonic power Doppler US with power Doppler US using a Doppler phantom under various parameter settings, focusing on the assessment of slow flow in the hyperechoic tissue. METHODS: While controlling the flow velocity (5 and 10 cm/s), pulse repetition frequency (500, 700, and 1,000 Hz), wall filter (low and medium), and Doppler gain (90%, 96%, and 100%), the authors performed both harmonic Doppler US and power Doppler US by using a Doppler phantom/flow control system. We measured and compared the relative intensities of the Doppler signals (0-250 scale) in both the vessels and hyperechoic tissue-mimicking materials with the two different imaging modalities. RESULTS: Power Doppler US with any combination of the four parameters evaluated depicted strong flow signals (mean, 213) that were superior to harmonic Doppler US (mean, 61). Relatively strong artifactual signals within the hyperechoic tissue-mimicking materials were noted on all power Doppler US studies (mean, 106) but nearly none on harmonic Doppler US (mean, 3). The contrast-to-noise ratio of harmonic Doppler US was significantly greater than that of power Doppler US. CONCLUSIONS: Harmonic Doppler US is more useful in assessing slow flow in hyperechoic tissue than power Doppler US because it produces fewer artifactual Doppler signals originating from stationary hyperechoic tissues, which can be misjudged as true signals on power Doppler US.

Blood Flow Velocity↗

PubMed1999

Physiological effects of constant versus variable power during endurance cycling.

PURPOSE: Previous theoretical research found that varying power slightly to counter external conditions may result in improved performance during cycling time trialing, but it is not known whether such power variations result in added physiological stress. Thus, the purpose of this study was to determine whether variable power (VP) cycling produced greater physiological stress than constant power (CP) cycling of the same mean intensity. METHODS: Eight trained male cyclists (age 28 +/- 2 yr, mass 74.4 +/- 2.3 kg, VO2max 4.24 +/- 0.13 L x min(-1), weekly training 277 +/- 44 km) performed three 1-h ergometer trials. The first trial was performed at a self-paced maximal effort. The mean power from that trial was used to determine the power for the CP trial (constant effort at mean power) and the VP trial (alternating +/- 5% of mean power every 5 min). RESULTS: No differences were found between the CP and VP trials in mean VO2 (CP 3.33 +/- 0.11 L x min(-1), VP 3.26 +/- 0.12 L x min(-1)), mean heart rate (CP 158 +/- 3 min(-1), VP 159 +/- 3 min(-1)), mean blood lactate concentration (CP 4.2 +/- 0.7 mM, VP 4.3 +/- 0.7 mM), or mean RPE (CP 13.9 +/- 0.4, VP 14.1 +/- 0.4). CONCLUSION: Therefore, during a strenuous 1-h effort (78% of VO2max), subjects experienced no additional physiological stress by varying power +/- 5% compared with that during a constant power effort.

Adult↗

PubMed2000

Cadence, power, and muscle activation in cycle ergometry.

PURPOSE: Based on the resistance-rpm relationship for cycling, which is not unlike the force-velocity relationship of muscle, it is hypothesized that the cadence which requires the minimal muscle activation will be progressively higher as power output increases. METHODS: To test this hypothesis, subjects were instrumented with surface electrodes placed over seven muscles that were considered to be important during cycling. Measurements were made while subjects cycled at 100, 200, 300, and 400 W at each cadence: 50, 60, 80, 100, and 120 rpm. These power outputs represented effort which was up to 32% of peak power output for these subjects. RESULTS: When all seven muscles were averaged together, there was a proportional increase in EMG amplitude each cadence as power increased. A second-order polynomial equation fit the EMG:cadence results very well (r2 = 0.87- 0.996) for each power output. Optimal cadence (cadence with lowest amplitude of EMG for a given power output) increased with increases in power output: 57 +/- 3.1, 70 +/- 3.7, 86 +/- 7.6, and 99 +/- 4.0 rpm for 100, 200, 300, and 400 W, respectively. CONCLUSION: The results confirm that the level of muscle activation varies with cadence at a given power output. The minimum EMG amplitude occurs at a progressively higher cadence as power output increases. These results have implications for the sense of effort and preferential use of higher cadences as power output is increased.

Adult↗

PubMed2001

Mutually exclusive muscle designs: the power output of the locomotory and sonic muscles of the oyster toadfish (Opsanus tau).

Animals perform a vast array of motor activities. Although it has generally been accepted that muscles are well suited to the function that they must perform, specialization for performing one function may compromise their ability for carrying out another. We examined this principle in the toadfish muscular system: slow-twitch red and fast-twitch white myotomal muscles are used for powering swimming at relatively low frequencies, while the superfast swimbladder muscle powers mating calls by contracting at 100 Hz. We measured muscle power output over a wide range of frequencies. The red and white locomotory muscles could not generate power over ca. 2.2 and 12 Hz, respectively and, hence, could not power sound production. In contrast, the swimbladder muscle has many specializations that permit it to generate power at frequencies in excess of 100 Hz. However, these specializations drastically reduce its power output at low frequencies: the swimbladder muscle generated only one-twentieth of the power of the red muscle and one-seventh of the power of the white muscle at the frequencies used during swimming. To generate the same total power needed for swimming would require unfeasibly large amounts of swimbladder muscle that could not fit into the fish. Hence, the designs of the swimbladder and locomotory muscles are mutually exclusive.

Action Potentials↗

PubMed2006

The power of a cylinder in an oblique meridian: revisiting an old controversy.

The sine-squared correlation states that the cylinder power in an oblique meridian forming an angle beta with the axis of the cylinder is reduced to sin(2)beta of the maximal power. The sine-squared relationship is fundamental in paraxial optics, but its validity has repeatedly been questioned during the last century. It appears that two powers are operative in an oblique meridian, curvital and torsional. Curvital power is responsible for refraction in the plane of the meridian, while the torsional component twists the light out of that plane. Curvital power is the traditional power concept, while torsional power has only recently been described. The long-standing criticism of the sine-squared correlation is based on the erroneous assumption that only curvital power is operational in paraxial imagery. Curvital and torsional power are both derived from the sine-squared correlation. The concept of these dual powers repudiates the criticism and is in complete accordance with paraxial optics.

Astigmatism↗

PubMed1996

Pump power loss and heat generation in a pivot bearing-supported Gyro centrifugal pump (C1E3).

Pump power loss is defined as input power that is not used for the output work of the pump. Less pump power loss means a higher pump efficiency. A common opinion is that the pump power loss is closely related to heat generation of the pump, which may affect not only the endurance of pump materials, but also blood damage in a blood pump. In this study, the relationship between pump power loss and heat generation in centrifugal blood pumps was investigated using the pivot-bearing supported Gyro C1E3 pump (C1E3) and Bio-Medicus pump (BP-80) under four different total pressure heat/flow conditions. A single special torque measuring driver motor was used for operating both the C1E3 and BP-80 in the four conditions. The pump power loss was calculated from the measured motor torque and hydraulic power. The changes in blood temperature were measured while the pump was operated at room temperature (25 degrees C) to obtain the following findings: First, the C1E3 caused less pump power loss and less temperature increase in blood than the BP-80 in all clinical simulated conditions that were tested; and second, the pump power loss and heat generation had a linear correlation with temperature rise from 22 to 25 degrees C in both the C1E3 and BP-80. During this period, approximately 30% of the pump power loss was transformed to heat, independent of the centrifugal blood pump type, provided that heat conduction through the pump housing and tubing was negligible during this particular period.

Animals↗

PubMed1987

Mechanical jumping power in young athletes.

Mechanical jumping power was determined for 286 young male athletes representing six sports events and ranging in calendar and skeletal ages from 8.8 to 17.1 and from 7.8 to 18.1 years, respectively. The subjects performed successive maximal vertical jumps on a contact mat for 30 s. The number of jumps and their cumulative flight time after 15 and 30 s were used for calculations of mechanical power. The jumping performances of the young athletes were found to be reproducible from the age of 10-12 years in respect to the angular displacement of the knee and duration of contact. Absolute mechanical power, as well as power related to body weight, increased with calendar and skeletal ages. Of the anthropometric characteristics, the circumference of the thigh and body weight showed the highest correlation with mechanical power; subjects with the greatest thigh circumference and body weight having the lowest mechanical power. The subjects were divided into 'power' (track and field, gymnastics) and 'endurance' (skiing, orienteering) groups. The former reached higher mechanical power values than the latter. Mechanical power for the second 15-s jumping period was on average 4.7% lower than for the first. The events did not differ from each other in respect of the decrease in power.

Adolescent↗

PubMed1994

Can power spectral analysis of heart rate variability identify a high risk subgroup of congestive heart failure patients with excessive sympathetic activation? A pilot study before and after heart transplantation.

BACKGROUND AND OBJECTIVES: Autonomic dysfunction seems to be involved in the progression and prognosis of severe congestive heart failure. Parasympathetic activity can still be abnormal 4-8 weeks after haemodynamic improvement by heart transplantation. To identify patients in heart failure with a more pronounced neural derangement and to analyse the changes in sympathetic and parasympathetic activity soon after heart transplantation, spectral indices of heart rate variability were assessed in 30 patients in severe heart failure and in 13 patients after heart transplantation; a group of 15 age-matched subjects served as controls. METHODS AND RESULTS: Heart rate variability was assessed by standard electrocardiography (ECG) in patients in heart failure and by oesophageal ECG in patients after heart transplantation. Compared with controls, the mean RR interval and total power were reduced in heart failure. The 30 patients showed two different patterns of heart rate variability: in 14 no power was detected in the low frequency band (0.03-0.15 Hz) (LF) and total power was mainly concentrated in the high frequency band (0.15-0.45 Hz) (HF), whereas in the remaining 16 patients power in the LF band was increased and power in HF band was reduced compared with the controls. Patients with undetectable LF had a lower mean RR interval and total power (745(25) v 864(36) ms, p < 0.05; 118(16) v 902(202) ms2, p < 0.001), higher concentration of plasma noradrenaline (635(75) v 329(54) pg/ml, p < 0.05), and worse clinical status and prognosis (4 deaths v no deaths at 6 month follow up) than patients with a dominant LF band. In the post-transplant patients both the mean PP interval of the remnant atrium and total power resembled results in the patients with heart failure; in 7 of the 13 post-transplant patients no power was detectable in the LF band: when both HF and LF power were present the results resembled those in the 16 patients in heart failure. CONCLUSIONS: These data suggest that in more advanced stages of congestive heart failure, power spectral analysis of heart rate variability allows identification of a subgroup of patients with higher sympathetic activation and poorer clinical status who are at major risk of adverse events. In the short term after cardiac transplantation the spectral profile of the rhythm variability of the remnant atrium was not improved, suggesting that parasympathetic withdrawal and sympathetic hyperactivity persist, despite the restoration of ventricular function.

Echocardiography, Transesophageal↗