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Biomedical subjects

D A Cunningham

Publications and source records attributed to D A Cunningham.

At least 73 records · Page 4Linked to original sources
PubMed1995

Estimation of arterial PCO2 in the elderly.

Arterial PCO2 (PaCO2), determined directly in the radial artery, was compared with indirect estimates of PCO2 in six elderly men (mean age 73.8 yr). Estimates of PaCO2 included arterialized venous PCO2 (PavCO2); end-tidal PCO2; mean alveolar PCO2, calculated by using a reconstruction of the alveolar oscillation in PCO2 and accounting for the presence of dead space (time-weighted mean for PCO2 throughout the respiratory cycle); and values calculated by using the empirical formula developed by Jones et al. (N. L. Jones, D. G. Robertson, and J. W. Kane. J. Appl. Physiol. 47: 954-960, 1979), which incorporates end-tidal PCO2 and tidal volume (PaCO2 derived from end-tidal PCO2 and VT). Measurements were made at rest and during cycle ergometry at 25 and 50 W while the subjects breathed various gas mixtures (euoxic-eucapnic, hypoxic-eucapnic, hyperoxic-eucapnic, and hyperoxic-hypercapnic). The mean differences between the estimates and the actual PaCO2 at rest and in 25- and 50-W exercise were as follows: PavCO2, 0.3 +/- 0.7 (SD), -0.1 +/- 0.7, and 1.8 +/- 1.2 Torr; end-tidal PCO2, 2.9 +/- 1.7, 4.0 +/- 3.1, and 3.7 +/- 3.2 Torr; time-weighted mean of alveolar PCO2, 2.6 +/- 1.9, 3.3 +/- 3.1, and 3.6 +/- 3.8 Torr; and PaCO2 derived from end-tidal PCO2 and VT, 2.4 +/- 1.3, 1.3 +/- 3.0, and 0.6 +/- 2.9 Torr. It is concluded that mean PavCO2 agreed most closely with mean PaCO2 both at rest and in exercise. All methods of deriving PaCO2 using measurements from the respired gases overestimated arterial values at rest. Of the noninvasive techniques, mean estimates calculated using the regression equation developed by Jones et al. corresponded most closely with PaCO2 in exercise.

Adult↗
PubMed1994

Local production of cytokines in the human cardiac allograft. A sequential study.

The observations of 2 types of CD4+ T cells (Th1 and Th2), which can be distinguished by their different cytokine profiles, has led to the possibility that analysis of cytokine profiles produced locally within transplanted allografts could be predictive of rejection or acceptance of that graft. We have investigated the expression of IL-2 and TNF beta (Th1 type cytokines), IL-4 and IL-10 (Th2 type cytokines), and the proinflammatory cytokines TNF alpha and IL-1 beta in sequential endomyocardial biopsies collected from 12 cardiac transplant recipients during the first 4 months after transplantation, by the analysis of RNA extracted from each biopsy by reverse transcriptase-polymerase chain reaction. The results obtained were compared with histopathological and clinical indicators of rejection. IL-2 was found in all severe (grade 3), in 57% of moderate (grade 2), in 21% of mild (grade 1) rejection, and in only 1 nonrejection (subsequently progressing to grade 3), where rejection was classified by routine histology. IL-4 and IL-10 were absent from grade 3 rejection, but present in 24% (IL-4) and in 17% (IL-10) of mild rejection and in a single nonrejecting biopsy, respectively. IL-4 was found in 2 cases of moderate rejection, and IL-10 in 1 case of moderate rejection. Statistical analysis showed that the presence of IL-2 positively correlated with both mild and moderate rejection, while IL-4 correlated with mild rejection (P < or = 0.05). IL-1 beta, TNF alpha, and TNF beta were found in both rejecting and nonrejecting biopsies, with no significant differences between the histological grades. Our results suggest that in the human situation, IL-2 and IL-4 may indeed be important in the modulation of rejection.

Base Sequence↗
PubMed1994

Oxygen uptake kinetics in cardiac transplant recipients.

Our purpose was to examine the gas exchange response to exercise in heart transplant (HT) patients and to characterize the O2 uptake kinetics (tau VO2) during successive square-wave on-transients from loadless cycling to moderate exercise. We hypothesized that with a slow heart rate response (and O2 transport limitation) O2 kinetics would be slowed but that with a repeated exercise initiated while the heart rate remained elevated the tau VO2 would be faster. Six male HT patients performed two ramp-function tests to determine peak O2 uptake (1.32 +/- 0.23 l/min) and ventilation threshold (1.02 +/- 0.16 l/min). Patients subsequently completed two repeats of a square-wave forcing function and repeated this on 2 days. Alveolar gas exchange was measured breath by breath. A monoexponential fit of signal-averaged data of the first exercise on-transient (between days) yielded a significantly slower tau VO2 in HT subjects than in healthy men (mean age 47 yr; n = 8) (77 +/- 26 vs. 45 +/- 4 s). With successive exercise (2nd transition) initiated while HR remained elevated the tau VO2 of HT patients was 46 +/- 17 s. The faster O2 kinetics of the second transition suggests that O2 delivery was enhanced and therefore that the tau VO2 may reflect bioenergetic processes controlling the rate of oxidative metabolism.

Blood Gas Analysis↗
PubMed1994

Ventilatory response to exercise in men and women 55 to 86 years of age.

This study examines the relationship between minute ventilation (VE) and carbon dioxide production (VCO2) during exercise in men (n = 128) and women (n = 96), 55 to 86 yr of age. The means for the slopes of VE-VCO2 (delta VE/delta VCO2), examined for graded exercise below the ventilation threshold (TVE), increased significantly for men (p < 0.0001), from 25.0 +/- 0.7 (SEM) at mean age 58 (55 to 59) yr to 32.2 +/- 1.8 at mean age 83 (80 to 86) yr, but did not change for women (p = 0.0812), from 22.3 +/- 0.9 at mean age 58 (56-59) yr to 24.2 +/- 2.4 at mean age 79 (75 to 85) yr. A correlation that was significantly greater than zero was found between delta VE/delta VCO2 and age. The increase in delta VE/delta VCO2 was 0.29/yr for men (r = 0.47, p < 0.001) and 0.20/yr for women (r = 0.28, p = 0.0051). In both cases, the explained variance was small (men = 22%; women = 8%). VE, tidal volume (VT), and breathing frequency (fb) were examined at VCO2 = 1.0 L/min, the highest intensity that most older men and women could exercise without exceeding TVE. VE was significantly higher by 14% in men 80 to 86 yr of age (38.2 +/- 1.4 L/min) compared with men 55 to 59 yr of age (33.5 +/- 0.8), whereas there were no differences in VE for the women.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1994

Clinical diagnosis from digital displays: results and conclusions from the St Mary's evaluation project.

Preliminary results with the first commercially available digital display system to be installed in a British radiology department were published in 1989: these consisted of data from observer performance studies of digitized images displayed using a 1024-line monitor, showing a single pathological feature--subperiosteal resorption in renal osteodystrophy. Further experiments have now been conducted with the successor to this equipment, a 1280-line digital display system. Formal observer performance studies were undertaken for four pathological conditions, and the results show statistically significant differences in performance between the digitized displayed images and those on film. The display system was not considered to be good enough for the task of primary radiological diagnosis of subtle lesions; findings support the conclusion that careful, objective clinical evaluation of digital display systems is important before they are introduced into clinical use.

Bone Resorption↗
PubMed1994

Verapamil improves left ventricular filling and exercise performance in hypertensive and normotensive elderly individuals.

OBJECTIVE: To study the effect of verapamil slow release (SR) upon left ventricular diastolic function and exercise capacity in newly diagnosed older hypertensive subjects compared with normotensive elderly and young controls. DESIGN: Cross-sectional prospective trial. INTERVENTIONS: Doppler echocardiography at rest and graded maximal exercise testing (with breath-by-breath gas analysis) before and 4 h after administration of oral verapamil SR 240 mg, and before and after 12 weeks of daily medication. MAIN RESULTS: Verapamil administration normalized resting blood pressure in the older hypertensive group, but did not alter blood pressure in older normotensive or young groups. Resting heart rate was not altered in any of the groups. Both the older hypertensive and normotensive groups showed improvement in measures of diastolic filling after verapamil ingestion. Specifically, the older hypertensive group showed significantly faster isovolumic relaxation time (IVRT). In the older normotensive group IVRT was not changed, but the E:A ratio (the ratio of early to late peak transmitral flow velocity) was increased after verapamil. No differences were observed between the effects of verapamil after acute ingestion (4 h) or with chronic use (12 weeks) in any of the variables measured. In the younger group diastolic filling was not altered after verapamil ingestion. In both the elderly normotensive and hypertensive groups maximum oxygen consumption was significantly improved following verapamil ingestion. Again, no differences were observed between 4 h and 12 weeks. In the younger subjects exercise performance was not changed after verapamil ingestion. CONCLUSIONS: Verapamil SR improved left ventricular diastolic function and exercise performance in hypertensive and normotensive elderly individuals. Verapamil normalized blood pressure in the hypertensive subjects, but did not alter blood pressure in the normotensive elderly or younger subjects.

Adult↗
PubMed1994

Exercise on-transient gas exchange kinetics are slowed as a function of age.

The purpose was to characterize gas exchange kinetics following the on-transient of exercise in men aged 30-80 yr. Forty-six men completed square wave exercise tests from loadless cycling to subventilatory threshold (V(E)T) work rates with gas exchange measured breath-by-breath. Signal averaged data were fit with a monoexponential equation to derive time constants (tau) for gas exchange and ventilation (tau VO2, tau VCO2, tau VE) and heart rate (tau HR). There was a significant slowing of ventilation and gas exchange kinetics across age with linear regression yielding an increase of 0.67 s.yr-1 for tau VO2 (39 s in young to 61 s in old), 0.57 s.yr-1 for tau VCO2, and 0.65 s.yr-1 for tau VE, whereas tau HR (44 to 41 s) was not changed significantly. The slowed VO2 kinetics with age may reflect limitations in muscle blood flow or in control of the rate of oxidative metabolism. The less marked slowing of tau VCO2 compared with tau VO2 across age may reflect reduced CO2 storage capacity with loss of muscle tissue. The tau VE change across age was similar to that for tau VCO2 (tau VE/tau VCO2 unchanged). The present study demonstrated marked age-related slowing of gas exchange dynamics at exercise onset.

Adult↗
PubMed1994

Effects of aerobic endurance training on gas exchange kinetics of older men.

The kinetics of gas exchange at the on-transient of exercise are appreciably slowed in older individuals. Eight older men (72 yr) completed 6 months of aerobic cycle training. Ventilation and gas exchange kinetics were determined at the onset of a below threshold (ventilatory threshold, V(E)T) square wave exercise function and compared with control values (N = 4, age 70 yr). Gas exchange data were measured breath-by-breath and signal averaged data were fit with a monoexponential function to determine the time constants (tau). The training group showed significant increases in VO2max (20%) and VO2 at V(E)T (21%). The tau for oxygen uptake kinetics decreased significantly (62.2 +/- 15.5 to 31.9 +/- 7.0 s). The tau VCO2 (70.9 +/- 10.9 to 43.8 +/- 11.4 s) and tau VE (89.2 +/- 18.0 to 50.4 +/- 11.3) also were significantly faster posttraining; however, tau HR (38.1 +/- 20.5 to 28.6 +/- 7.2) was not significantly altered. Thus, with a vigorous training program, the kinetics of gas exchange of older individuals were faster, and approached values reported in fit young subjects.

Aged↗
PubMed1993

Strength training alters contractile properties of the triceps brachii in men aged 65-78 years.

Voluntary and electrically evoked contractile properties were studied in the triceps brachii following a 24-week dynamic strength training program in ten men aged 65-78 years. Eight men of a similar age were control subjects. A resistance overload program was undertaken three times per week with subjects performing four sets of six to eight repetitions at 80% of their one repetition on maximum (1RM). Maximum voluntary contraction (MVC) and contractile properties were measured at 0, 12, and 24 weeks in the exercise group and at 0 and 24 weeks in the controls. The 1RM was used to assess dynamic strength at 0 and 24 weeks in the exercise group. Contractile measures consisted of supramaximal isometric twitch and post-activation twitch parameters. Muscle size was estimated from anthropometric measurements. Compared with the control group, the exercise group MVC increased by about 20% and time to peak tension was slowed by about 11%. Also in the exercise group the peak rate of torque development of the potentiated twitch was reduced by about 10%. Twitch potentiation was substantial in both groups (about 140%) and unaffected by training. The 1 RM increased by about 30%, and there was a non-significant positive change of 8.6% in the muscle plus bone cross-sectional area in the exercise group. The results show that the force generating capacity of the triceps brachii in these men can be significantly improved for up to 24 weeks using concentric overload training. Furthermore, the finding of slowed twitch properties and no change in peak twitch amplitude substantiate and extend the limited data currently available on intrinsic contractile changes in the elderly.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1993

Gas exchange dynamics with sinusoidal work in young and elderly women.

The objective of this study was to model the dynamics of, and interrelationships among, gas exchange, ventilation, and heart rate responses to sinusoidal forcing in young and elderly women. Nineteen females, 22-28 years (n = 10) and 62-73 years (n = 9) volunteered for the study. All experiments were conducted at work rates below the ventilatory threshold (TVE). A sine wave test consisted of 4 min of cycling (60 rpm) at a work rate equal to the mean of the limits of sinusoid (60% TVE) followed by 16-20 min of a sinusoidally varying work rate (30-90% of TVE) and ending with 4 min of cycling at 60% TVE. The periods were 0.75, 1.0, 1.5, 3.0, 6.0, 10.0 min, assigned randomly. The averaged data were used to determine amplitude and phase lag of the sinusoidal response of VO2, VCO2, VE, fH, PETCO2, and PETO2. Bode plots demonstrated that the dynamics of the cardiorespiratory responses were all well-described by a first-order exponential equation with a delay for both young and elderly subjects. The time constants were much longer in the elderly. Nevertheless, there appeared to be a strong link between the relative slowing of the four components of the gas transport system (VO2, VCO2, VE, and fH). This may suggest one single factor is reflected in the slowing of all components in older subjects.

Adult↗
PubMed1993

Determinants of independence in the elderly.

The purpose of this study was to compare strength, flexibility, and cardiorespiratory fitness of the elderly living independently (n = 64) with those in rest or nursing homes (n = 61), and to identify those variables most strongly associated with an independent lifestyle. Quantitative levels of independence (Incapacity Index) and of activity were determined by questionnaires. Flexibility was measured using the Leighton Flexometer. Strength was measured using a modified sphygmomanometer. Cardiorespiratory fitness was measured using a self-paced walking test. Body size factors were also determined. Independent and dependent subjects were significantly different in age, which imposed a limitation on interpretation of these data. However, this factor was accounted for statistically in the analyses. Independent individuals compared to dependent ones showed significantly greater flexibility, activity levels, and choice of walking speed. Through multiple regression analysis, it was found that 40% of the variance in Incapacity Index was associated with participation in outdoor activities, greater shoulder flexibility, and a faster normal walking speed (> 1.0 m.s-1).

Activities of Daily Living↗
PubMed1993

Anthropometric and computed tomographic assessment of the thigh in young and old men.

Anthropometric (AP) and computed tomographic (CT) methods of determining limb and muscle-plus-bone cross-sectional area (CSA) and volume (Vol) were compared in 13 young (M = 24.5 yrs) and 11 old (M = 71.0 yrs) men. CSA of total thigh, muscle-plus-bone, quadriceps, and hamstring muscle compartments and muscle were measured from CT scans. Corresponding muscle Vol were estimated from anthropometric equations. Prediction equations for CT measures were developed from AP measures using multiple linear regression. AP and CT techniques produced different values for thigh component CSA and Vol, especially in the old men. AP overestimated muscle-plus-bone CSA and Vol (4-6%) and underestimated skin and subcutaneous tissue CSA and Vol (17-33%). Prediction equations for quadriceps CSA and Vol (R2 = 80-96%) were more accurate than equations for hamstrings (R2 = 42-65%). Specific thigh muscle CSA and Vol can be predicted from AP measures (SEE 5-15%). These findings may have clinical significance when normalizing strength per unit of muscle size.

Adult↗
PubMed1993

Evaluation of the VMM turbine for spirometry in the applied physiology laboratory.

The volume measurement module turbine (VMM) was evaluated in 51 subjects for spirometry in applied physiology against the Stead-Wells spirometer (SW) and Wright peak flow meter (WM). The volume and flow ranges (VMM) were, FEV1 1.32 to 3.94 L (mean 2.62, confidence interval [CI] 2.46 to 2.78); forced vital capacity (FVC) 1.97 to 5.06 L (mean 3.50, CI 3.29 to 3.71); and peak expiratory flow rate (PEFR) 290 to 624 L.min-1 (mean 434, CI 407 to 461). The mean difference for FEV1 was 0.09 L (CI 0.05 to 0.14), FVC 0.04 L (CI -0.02 to 0.10), and PEFR 18.0 L min-1 (CI 8.7 to 27.3) less than SW or WM. Bias with FEV1 and FVC was not significant, though PEFR demonstrated a significant proportional error. The repeatability coefficients for FEV1 and FVC were 0.18 and 0.20, comparable to the SW; but for PEFR they were greater, 58.4 versus 33.8 L.min-1 by WM. The VMM turbine is accurate and reliable for the measurement of FEV1 and FVC over the ranges studied; however, care should be taken when interpreting PEFR.

Adult↗
PubMed1993

Cardiac output and left ventricular function in response to exercise in older men.

Studies of the cardiovascular response to exercise in older subjects have presented conflicting data regarding left ventricular function, the cardiac output-oxygen consumption (Q-VO2) relationship, and the pattern of change in Q, stroke volume (SV), and arteriovenous O2 difference. We have examined the cardiovascular response to submaximal and strenuous exercise in 96 men of mean age 63 years during an incremental treadmill test with Q determined by CO2 rebreathing, and in 12 subjects studied during incremental supine exercise with left ventricular volumes evaluated by radionuclide angiocardiography. During treadmill exercise the Q was approximately 10% lower than reported for younger samples, with a lower intercept of the Q-VO2 relationship. During near-maximal exercise Q was approximately 15 L.min-1, with SV of 95 mL plateauing or showing a small decline in heavy work. Peak arteriovenous O2 difference (150 + mL.L-1) approached values of the young. During the supine exercise SV increased from rest to exercise, with a consistent increase in ejection fraction (rest, 66%, to peak exercise, 76%). In contrast to a prior report, the end-diastolic volume was constant, with the increase of SV attributable to a reduced end-systolic volume. Also, in contrast to a number of reports in older subjects, our findings show only small losses in cardiovascular response, and in left ventricular performance during light through strenuous exercise.

Aged↗
PubMed1993

Ventilatory sensitivity to CO2 in hyperoxia and hypoxia in older aged humans.

Findings from studies of the effects of aging on the human respiratory controller are equivocal. This study assessed the ventilatory response to CO2 in hyperoxia and hypoxia in groups of younger (YS) and older (OS) humans. Two protocols were used. In the first, end-tidal PCO2 (PETCO2) was clamped at 1-2 Torr above rest (eucapnia), and, in the second, PETCO2 was clamped at 7-8 torr above resting PETCO2 (moderate hypercapnia). End-tidal PO2 was clamped at 100 Torr throughout except for two 2-min periods at 500 and 50 Torr. The ventilatory responses for each subject at each PO2 were fitted to the linear equation, VE = S(PETCO2 - B), where VE is minute ventilation, S is the response curve slope, and B is the response curve threshold. In eucapnia, there were no differences in hypoxic and hyperoxic VE between YS and OS. In hypercapnia, hypoxic VE was 24% lower in OS [39.93 +/- 2.71 (SE) l/min] than in YS (52.16 +/- 3.17 l/min). In hypoxia, S was significantly lower in OS (3.25 +/- 0.38 l.min-1.Torr-1) than in YS (4.76 +/- 0.37 l.min-1.Torr-1). We conclude that, in older humans, VE is lower in hypoxia during moderate hypercapnia, resulting mainly from a decreased peripheral chemoreflex CO2 sensitivity.

Adult↗
PubMed1992

Influence of ageing on aerobic parameters determined from a ramp test.

The purpose of this study was to examine the four parameters of aerobic function, the maximum oxygen uptake (VO2max), ventilation threshold (ThVE), efficiency, and the effective time constant for oxygen consumption (tau'VO2), across age. In particular, the study was designed to observe whether there may be accelerated declines in aerobic function beyond 60 years of age. Seventy-nine sedentary men aged 30-84 years were studied. Each subject performed two maximal cycle ramp function tests, and data were collected on a breath-by-breath basis. The VO2max, from a plateau in VO2, was achieved in 87% of the subjects using the ramp test. The VO2max showed a significant decrease with increasing age (from linear regression, r = -0.81) at a rate averaging 0.037 l.min-1.year-1. The ThVE also declined with increasing age, but at a slower rate (0.013 l.min-1.year-1). The tau'VO2 was significantly increased across the age groups from 69 s for those aged 30-40 years to 98 s for those aged 60 years or more. There was no evidence of accelerated decline in these aerobic parameters beyond age 60 years, and there were no differences in efficiency (27.5-29.9%) across age. Although other forcing functions should be used to confirm this characterization of the oxygen kinetics, this slowed response with age would result in greater oxygen deficit and possibly earlier fatigue in response to even light exercise in older individuals.

Adult↗