PubMed Health⌕ Search

Biomedical subjects

D A Cunningham

Publications and source records attributed to D A Cunningham.

At least 55 records · Page 3Linked to original sources
PubMed1997

Duplex scanning in the postoperative surveillance of patients undergoing total hip arthroplasty.

Color flow duplex imaging is a well-established method for the diagnosis of deep vein thrombosis in symptomatic patients; however, the sensitivity and specificity of duplex scanning compared with venography in high-risk asymptomatic patients are not known. Consecutive patients undergoing total hip arthroplasty who consented to have bilateral venography on days 8 to 12 were included in this prospective study. One hundred and fifty-one venograms were finally obtained in 78 patients. All duplex scanning was performed with the Ultramark 9 ATL (Advanced Technology Laboratories) by one investigator. In the beginning of the study, the first 44 legs, only the femoropopliteal segment was tested and the result was based on B-mode compression; the sensitivity for the duplex was 56% (5/9), and the specificity, 94% (33/35). In the next 107 legs, the addition of color to our criteria improved the sensitivity of the duplex scan from 55% to 93% (13/14) for the femoropopliteal segment and the specificity from 94% to 99% (92/93). For the calf segment, in the same 107 legs, using the color facility of the duplex, the sensitivity and specificity were 79% (15/19) and 97% (85/88), respectively. The color facility of new-generation machines makes duplex scanning reliable for the detection of proximal deep vein thrombosis, even in asymptomatic high-risk patients. For the detection of calf deep vein thrombosis, however, more experience is needed. A larger study is necessary to confirm these preliminary data.

Aged↗
PubMed1997

The effects on cardiac arrhythmias of antihypertensive therapy causing regression of left ventricular hypertrophy.

To examine the effects of antihypertensive therapy causing regression of left ventricular hypertrophy on cardiac arrhythmias, 26 hypertensive subjects were treated with ramipril with felodipine if required, and followed for 6 months after blood pressure control. Compared with baseline, left ventricular mass index (LVMI) was significantly reduced both at blood pressure control and after a further 6 months of treatment (baseline, blood pressure control, 6 months after blood pressure control; LVMI 142 +/- 3.6, 131 +/- 3.4, 123 +/- 3.8* g/m2, *P < .01 compared with baseline). There was a significant relationship between the decrease in systolic blood pressure and the decrease in LVMI after 6 months of blood pressure control compared with baseline (r = 0.41, P = .05). Compared with baseline, the average total number of ventricular ectopics decreased after blood pressure was controlled (88 +/- 59 and 21 +/- 12 respectively); however this reduction was not maintained after 6 months of further treatment, either before (78 +/- 50) or after drug washout (86 +/- 40). Compared with baseline (639 +/- 590) supraventricular ectopic total was not initially reduced after blood pressure control (650 +/- 604), but was reduced after a further 6 months of treatment (294 +/- 261). This reduction was maintained after drug washout (267 +/- 254), although this did not reach statistical significance. Radionuclide scanning at baseline was not a predictor of patients with the highest risk of arrhythmia and there was no correlation between improvement or worsening of a defect with changes in ventricular ectopic total. In conclusion, antihypertensive therapy with ramipril and felodipine, although causing regression of left ventricular hypertrophy did not lead to a sustained reduction in ventricular ectopic total.

Adult↗
PubMed1997

Oxygen costs using a reciprocating gait orthosis in a paraplegic (T9) patient with a bilateral below-knee amputation: case report.

The Reciprocating Gait Orthosis (RGO) is a useful aid to ambulation for patients with paraplegia. Its use has been described previously though not in conjunction with limb prostheses. We report here the energy costs of ambulation of a patient, disabled by paraplegia at T9 and bilateral below-knee amputations, walking at her preferred rate using an RGO while gas exchange was measured by the Douglas bag method. Oxygen uptake (VO2) rose from 0.198 1 min-1 at rest to 0.582 1 min-1 in the last minute of exercise, representing a VO2 of 14.3 ml kg-1 min-1. During the fourth minute of ambulation, energy consumption was 30.44 J kg-1 s-1 with an energy cost of 4.17 J kg-1 m-1 at a velocity of 0.13 m s-1, Ambulation with this combination of disability is possible with the aid of limb prostheses and an RGO though it is slow and the energy expenditure as consumption per second and cost per metre are high.

Adult↗
PubMed1997

Effects of 5-day exercise training in elderly subjects on resting left ventricular diastolic function and VO2max.

We evaluated the effects of short-term, high-intensity exercise training and detraining on resting left ventricular diastolic function (LVDF) and maximal aerobic power (VO2max) in 7 sedentary older (age = 68 +/- 4 years) men (n = 5) and women (n = 2). Training consisted of cycling for 60 min with power output set at 70% (Day 1), 80% (Day 2), and 90% (Days 3-5) of the pretraining peak work rate. Detraining consisted of a return to regular exercise habits. LVDF increased 10% in the early (E) flow velocity, decreased 18% in the late (A) flow velocity wave, and decreased 31% in the isovolumic relaxation time. VO2max was increased 12% while plasma volume (PV) increased 10% following training and returned to baseline after detraining. The exercise-induced change in VO2max was directly related to the change in E/A (r = .52) and indirectly related to the change in IVRT (r = -.62). It was concluded that short-term, high-intensity exercise training improves LVDF and is tolerated well in older subjects, and that the calculated changes in PV and aerobic power are similar to those observed previously in a younger population.

Aged↗
PubMed1997

Dynamics of the ventilatory response to step changes in end-tidal PCO2 in older humans.

The purpose of this study was to examine the ventilatory response to carbon dioxide (CO2) in young and older men. Six square-wave steps of end-tidal CO2 (PETCO2) were administered in euoxia (PETO2 = 100 torr), hyperoxia (PETO2 = 500 torr), and mild hypoxia (PETO2 = 60 torr). The peripheral and central chemoreflex loops were described by three parameters including a gain (gp and gc), time constant of the response (tau p, tau c), and a time delay (Tp, Tc), respectively. The young and older men showed similar characteristics for Tp and Tc, with Tp being 3 to 5 s shorter than Tc. In hypoxia, the ventilatory responses of the old group were characterised by a significantly smaller gc and a smaller gp. In hypoxia, tau c was significantly shortened from its euoxic value in the young group, but not in the old group. Thus, this study demonstrated that in older men, the ventilatory responses to CO2 in euoxia and hyperoxia are similar to younger men, while in hypoxia the ventilatory responses are characterised by smaller gain terms.

Adult↗
PubMed1997

A model of oxygen transport capacity changes for independently living older men and women.

The purpose of the present investigation was to describe, for a subset of a large random survey of men and women, restricted to the ages of 55 to 85 years, the physiological decay pattern for aerobic fitness and contributing factors of cardiovascular and pulmonary function. The time course of the age-related changes in maximal oxygen uptake (VO2max), ventilatory threshold (TVE), maximal ventilation (VEmax), maximal heart rate (HRmax), and O2 pulse (VO2max/HRmax) were examined by fitting the data to a decaying exponential model by use of a least-squares parameter estimation technique. The time constant (tau) was used to describe the rate of decline. The women showed a much slower decline in VO2max (tau = 47.4 years) and TVE (tau = 83.3 years) than the men (tau = 20.8 and 15.4 years, respectively). There was a significant age-related decrease in body weight (0.45 kg.yr-1) in the men, whereas the women showed no change. Pulmonary function did not limit performance based on the very slow decline in VEmax and the normal FEV1.0. The decay in HRmax was better described by a linear model, resulting in an extremely slow tau. Maximal O2 pulse clearly exhibited an exponential decay, with a shorter tau (tau men = 13.5 years; tau women = 28.5 years) than any other variable.

Aged↗
PubMed1997

Muscle capillarization O2 diffusion distance, and VO2 kinetics in old and young individuals.

The relationships between muscle capillarization, estimated O2 diffusion distance from capillary to mitochondria, and O2 uptake (VO2) kinetics were studied in 11 young (mean age, 25.9 yr) and 9 old (mean age, 66.0 yr) adults. VO2 kinetics were determined by calculating the time constants (tau) for the phase 2 VO2 adjustment to and recovery from the average of 12 repeats of a 6-min, moderate-intensity plantar flexion exercise. Muscle capillarization was determined from cross sections of biopsy material taken from lateral gastrocnemius. Young and old groups had similar VO2 kinetics (tau VO2-on = 44 vs. 48 s; tau VO2-off = 33 vs. 44 s, for young and old, respectively), muscle capillarization, and estimated O2 diffusion distances. Muscle capillarization, expressed as capillary density or average number of capillary contacts per fiber/average fiber area, and the estimates of diffusion distance were significantly correlated to VO2-off kinetics in the young (r = -0.68 to -0.83; P < 0.05). We conclude that 1) capillarization and VO2 kinetics during exercise of a muscle group accustomed to everyday activity (e.g., walking) are well maintained in old individuals, and 2) in the young, recovery of VO2 after exercise is faster, with a greater capillary supply over a given muscle fiber area or shorter O2 diffusion distances.

Adult↗
PubMed1996

Nature of the interaction between central and peripheral chemoreceptor drives in human subjects.

The purpose of the current study was to investigate the nature of the interaction between the central and peripheral chemoreflex loops in humans, using the different speeds of response of the central and peripheral chemoreceptors to enable a temporal separation of their chemical stimulation. Subjects were exposed to an end-tidal Pco2 of 8-10 torr (1 torr = 1 mmHg = 133.3 Pa) above resting Pco2, with end-tidal Po2 = 100 torr, for 8 min. Thirty seconds after the hypercapnic stimulus was withdrawn, a 5-min hypoxic stimulus (end-tidal Po2 = 50 torr) was introduced. The 30-s interval was believed to be sufficient time for the peripheral chemoreceptors to adapt to the new level of carbon dioxide. Over the subsequent 5 min of hypoxia, however, the central chemoreceptors were exposed to diminishing hypercapnia. The response to the hypoxic step was compared with the effect of the same hypoxic step without the preceding period of hypercapnia. In 4 of the 5 subjects studied, the ventilatory response to hypoxia was unaffected by relative hypercapnia at the central chemoreceptor, suggesting that the central and peripheral chemoreflexes were independent of each other.

Adult↗
PubMed1996

The influence of age and cardiorespiratory fitness on kinetics of oxygen uptake.

The purpose of this study was to determine the influences of ageing and cardiorespiratory fitness on kinetics of VO2 during the transition to exercise of moderate intensity. Subjects performed three transitions to and from a 6-minute square wave constant load, at an intensity corresponding to 90% of ventilatory threshold (VET), to determine VO2 kinetics. The young group had a significantly faster time constant of VO2 (tau VO2). Tau VO2 was significantly correlated with VO2max for both young and old groups; however, the slope of the tau VO2--VO2max regression equation was steeper for the old group, indicating that fit older subjects had VO2 kinetics that approached those of fit young. A multiple linear regression indicated that relative fitness was the strongest significant predictor of tau VO2, followed by sex and age. Although VO2 kinetics are definitely slowed with age, relative levels of cardiorespiratory fitness also have a great influence on the dynamic response of VO2.

Adult↗
PubMed1996

Peripheral chemoreflex drive in moderate-intensity exercise.

The purpose of this study was to measure the contribution of the peripheral chemoreceptor (pR) to VE during the steady-state of moderate-intensity cycle ergometer exercise using continuous hyperoxic suppression of pRc drive, while stabilizing the drive from the central chemoreceptor by clamping end-tidal PCO2 (PETCO2) at the peak level attained during the hyperoxic period of a poikilocapnic ride. In the isocapnic protocol, the PETCO2 was maintained at a constant level by a negative feedback, open loop system. Five subjects completed four repetitions of each of the poikilocapnic and isocapnic protocols. In the poikilocapnic protocol, VE declines following the step into hyperoxia and then began to increase, whereas the decline in VE was maintained in the isocapnic protocol. However, the mean decrease in VE was not significantly different between the poikilocapnic (16.1 +/- 5.0%) and isocapnic (14.9 +/- 4.4%) protocols. These results suggest that the declining phase of VE is fully complete before the secondary central stimulating actions of hyperoxia on VE and that the pRc contributes about 15% of the drive to breathe in moderate intensity exercise.

Adult↗
PubMed1996

Kinetics of pulmonary oxygen uptake and muscle phosphates during moderate-intensity calf exercise.

The purpose of this study is to directly compare the dynamic responses of phosphocreatine (PCr) and P(i) to those oxygen uptake (VO2) measured at the lung during transitions to and from moderate-intensity exercise. Changes in PCr and P(i) were measured by 31P-nuclear magnetic resonance spectroscopy, and changes in VO2 were measured breath by breath by mass spectroscopy during transitions to and from moderate-intensity square-wave ankle plantar flexion exercise in 11 subjects (7 men and 4 women; mean age 27 yr). Three repeated transitions were averaged for improvement in signal-to-noise ratio of phosphate data, and 12 transitions were averaged for VO2 measurements. Averaged transitions were fit with a monoexponential curve for determination of the time constant (tau) of the responses. Mean tau values for on transients of PCr, P(i), and phrase 2 VO2 were 47.0, 57.7, and 44.5 s, respectively, whereas means tau values for off transients were 44.8, 42.1, and 33.4 s, respectively. There were no significant differences between tau values for phosphate- and VO2-measured transients or on and off transients. The similarity of on and off kinetics supports linear first-order respiratory control models. Measurement of phase 2 pulmonary VO2 kinetics to and from moderate-intensity small-muscle-mass exercise reflect muscle phosphate kinetics (and muscle oxygen consumption).

Adult↗
PubMed1996

Cardiorespiratory kinetics during exercise of different muscle groups and mass in old and young.

The purpose was to compare cardiorespiratory kinetics during exercise of different muscle groups (double-leg cycling vs treadmill walking and single-leg ankle plantar flexion) in old and young subjects. Oxygen uptake (VO2) during exercise transitions was measured breath by breath, and the phase 2 portion of the response was fit by a monoexponential for determination of the time constant (tau) of VO2. Two separate studies were performed: in study 1, 12 old (age 66.7 yr) and 16 young (aged 26.3 yr) subjects were compared during cycling and ankle plantar flexion exercise, and in the study 2, five old (aged 69.6 yr) and five young (24.4 yr) subjects were compared during cycling and treadmill walking. VO2 transients during square-wave cycling exercise were significantly slower in the old compared with the young groups. In contrast, VO2 kinetics did not differ between old and young groups during plantar flexion exercise. Heart rate (HR) kinetics followed the same pattern, with tau HR being significantly slower in the old vs young groups during transitions to cycling but not to plantar flexion. In study 2 tau VO2 and tau HR during on-transients to treadmill square-wave exercise were significantly slower in the old group compared with the young group, but tau VO2 was significantly faster during treadmill exercise than during cycling in the old group. The differences with aging between the modes of exercise may be related to the muscle mass involved and the circulatory demands. On the other hand, slowed VO2 kinetics with age appear to occur in a mode (cycling) in which the muscles are not accustomed to the activity, whereas in a mode of normal activity (walking) and with the muscle groups (plantar flexors) accustomed to the activity, VO2 kinetics are not slowed to the same degree with age.

Adult↗
PubMed1996

Deep venous thrombosis prophylaxis with low molecular weight heparin and elastic compression in patients having total hip replacement. A randomised controlled trial.

Seventy-eight patients having elective total hip replacement were randomised into 3 groups A) control; B) low molecular weight heparin: (enoxaparin 40 mg once daily) and C) enoxaparin (40 mg once daily) plus graduated elastic compression (TEDR stockings) for 8-12 days. All patients had a preoperative perfusion lung scan and chest X-Ray and a postoperative perfusion/ventilation scan together with bilateral ascending venography on days 8-12. A blood sample was taken preoperatively, on the 1st, 3rd and 5th postoperative day and at the end of the study. The control group received placebo injections. The venograms and V/Q scans were reported blindly by an independent panel of three and one radiologists respectively. An independent panel of assessors stopped entry in the control group when a total of 45 patients were admitted according to Ethics Committee directives. The study continued with groups B and C. The incidence of DVT (including isolated asymptomatic calf thrombi) was as follows: Group A (n = 14) 93%; Group B (n = 32) 38%; Group C (n = 32) 25% (chi 2; p < 0.001 for group A versus B or C). The incidence of proximal DVT was: Group A 57%; group B 28%; group C 13% (chi 2; p = 0.057 for group A versus B and p < 0.005 for group A versus C). The incidence of silent pulmonary embolism (PE) (new defect on V/Q scan) was 28% (8 out of 29) in patients with and 5% (2 out of 43) in patients without DVT (chi 2; p < 0.02). The combination of high TAT and low anti-Xa activity on the 1st postoperative day identified a high risk group of patients who had a 56% incidence of proximal DVT on the 8th to 12th postoperative day. Further studies are needed to confirm the suggested increased efficacy in prophylaxis by the combination of LMWH and GEC as compared with LMWH alone.

Aged↗
PubMed1995

V/Q defects and deep venous thrombosis following total hip replacement.

Seventy-two patients undergoing elective total hip replacement were studied with bilateral venography, pre-operative and post-operative lung scans. Twelve belonged to a control group that received placebo injections and 60 patients to treatment groups that received low molecular weight heparin. The incidence of deep venous thrombosis was 11 (92%) of 12 patients in the control group and 18 (30%) of 60 patients in the treatment group (X2: P < 0.001). The incidence of pulmonary embolism (new unmatched perfusion defects) was five (42%) of the 12 patients in the control group and five (8.3%) of the 60 patients in the treatment groups (X2: P < 0.002). The incidence of pulmonary embolism (new unmatched perfusion defects) was eight (27.5%) of 29 patients with deep venous thrombosis and two (4.6%) of 43 without deep venous thrombosis (X2: P < 0.02). Of the ten patients who had pulmonary embolism according to this study's criteria (one or more new defect on perfusion, unmatched on the ventilation scan), eight would have been classified as high probability by the Biello criteria, and only five by the PIOPED criteria, if the pre-operative scans were not available. We conclude that having a pre-operative lung scan improves ability to interpret the postoperative lung scans in high risk patients.

Elective Surgical Procedures↗
PubMed1995

Sleep deprivation: effects on work capacity, self-paced walking, contractile properties and perceived exertion.

The primary purpose of this study was to examine the effect of a 48-hour period of sleep deprivation on the performance of selected physical work tasks [30-45% of maximum oxygen consumption (VO2max)]. In addition, this study assessed the effect of continual performance of physical work during sleep deprivation on standardized physiological and psychological test scores. Nineteen male subjects performed six different physical tasks, designed to involve all major muscle groups, during a 48-hour period of sleep deprivation. Fourteen subjects served as sleep-deprivation controls. Performance on all physical work tasks decreased significantly. Neither sleep deprivation (SD) or sleep deprivation in conjunction with continuous physical work (SDW) had any effect on muscle contractile properties, anaerobic power measures or resting blood glucose and lactate concentrations. Only SD subjects demonstrated a decline in cardiorespiratory function. Self-selected walking pace decreased and perceived exertion increased significantly in the SDW group. Positive and negative mood scores were adversely affected in both groups, the total change being greatest in SD subjects. The results indicate that performance of physical work tasks requiring 30-45% VO2max declines significantly over a 48-hour period of sleep deprivation. However, maximal physiological function is not unduly compromised by either the work tasks in conjunction with sleep deprivation or by sleep deprivation alone.

Adult↗