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Biomedical subjects

D A Cunningham

Publications and source records attributed to D A Cunningham.

At least 19 recordsLinked to original sources
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↗
PubMed1992

Cardiorespiratory adaptation with short term training in older men.

The purpose of this study was to assess the rate of training-induced cardiorespiratory adaptations in older men [mean (SD), 66.5 (1.2) years]. The eight subjects trained an average of 4.3 (0.3) times each week. The walk/jog training was in two phases with 4 weeks (phase 1) at a speed to elicit 70% of pre-training maximal oxygen consumption (VO2max), and 5 weeks (phase 2) at 80%. Maximal exercise treadmill tests and a standardized submaximal protocol were performed prior to training, at weekly intervals during the training programme, and after training. VO2max (ml.kg-1.min-1) increased significantly over both phases: 6.6% after the first 4 weeks, and an additional 5.2% after the final 5 weeks. The weekly changes in VO2max over phase 1 were well fitted by an exponential association curve (r = 0.75). The half-time for the rate of adaptation was 13.8 days, or 8.3 training sessions. Over phase 2, the change in VO2max did not plateau and a time course could not be determined. Submaximal exercise heart rate (fc) was reduced a significant 10 beats.min-1 after the first 4 weeks, and further 6 beats.min-1 over the final 5 weeks. The fc reductions showed half-times of 9.1 days (phase 1) and 9.8 days (phase 2) (or 5-6 training sessions). The anaerobic ventilation threshold was increased 13.9% over the 9 weeks of training and the respiratory exchange ratio during constant load heavy exercise was significantly reduced; however, these changes could not be described by an exponential time course. Thus, short-term exercise training of older men resulted in significant and rapid cardiorespiratory improvements.

Adaptation, Physiological↗
PubMed1992

Physiological responses of young and elderly men to prolonged exercise at critical power.

The critical power (CP) of a muscle group or individual may represent the highest rate of work which can be performed for an extended period. We investigated this concept in young (n = 13, 24.5 years) and elderly (n = 12, 70.7 years) active men by first determining CP and then comparing responses elicited by 24 min of cycle exercise at power outputs (omega) corresponding to CP. Values from the final 2 min of the 24-min ride were expressed relative to maximal values established in a ramp test. CP for the elderly was only 65% that for the young, but on a relative basis, it was significantly higher both in terms of omega (67 vs 62% of omega max) and oxygen consumption (VO2) (91.5 vs 85.2% of maximum oxygen consumption). There were no group differences in relative values for ventilation (VE), heart rate or respiratory exchange ratio (R). During the 24-min ride, VO2 and R achieved a plateau in both groups, while VE, blood lactate and arterial PCO2 continued to change in the young. It was concluded that CP can be determined in active elderly men, but that CP may not represent a true non-fatiguing work rate in either young or elderly men.

Adult↗
PubMed1992

Age and sex effects on mobility of the human ankle.

We investigated whether values for passive resistive torque, dorsiflexion strength, and active mobility of the ankle joint varied with age in a randomly selected sample of middle-aged and elderly males and females. The main effects of sex and age group were significant, without an interaction effect, on values for passive resistive torque and voluntary strength. The trends indicated that females had lower values for both variables and that passive torque increased and strength decreased with respect to age. Dorsiflexion range of motion also showed a highly significant trend to decrease across age groups, and more so for females than males. Mean values for middle-aged men vs old men went from 20.0 to 13.5 degrees, while corresponding values for women decreased from 20.7 degrees of dorsiflexion to 10.1. Functional ankle movement thus becomes limited with age, but could be improved by strengthening weak dorsiflexor muscles.

Aged↗
PubMed1992

Forced expiratory volume, height, and demispan in Canadian men and women aged 55-86.

In a random cross-sectional study in London, Canada, forced expiratory volume in 1 second (FeV1.0), height, and demispan (fingerweb to central sternal notch) were measured on 182 men and 212 women of mean ages 70.4 (SD 8.5) and 71.3 (8.2). The mean FeV1.0 for men was 2.55 (0.66) l, and for women 1.80 (0.48) l and declined 29 ml.year-1 and 25 ml.year-1, respectively. The mean FeV1.0 standardized for measured height and calculated height for men was 2.54 (0.61) l and 2.55 (0.62) l in men, and 1.80 (0.46) l and 1.79 (0.45) l in women. There was no significant difference between the two methods of standardization, and the relationship of height to demispan in this independent elderly population was constant across age for both men (2.16) and women (2.17). Linear and proportional regression coefficients to predict FeV1.0 from height and demispan have been generated for this random sample aged 55 to 86 years.

Aged↗
PubMed1992

Response rates in a survey of physical capacity among older persons.

A representative sample of 420 subjects aged 55 to 84 was sought for participation in a study of the relationship between physical activity and health. A stratified random sample with 35 subjects in each of 12 age-gender categories was designed, using lists generated consecutively until the target number for each category was reached. Although the protocol required walking and treadmill tests, 60.3 percent of those eligible participated, a figure comparable to that of NHANES II and superior to that of the Canada Fitness Survey. Participants were younger, more likely to be male, less likely to be currently married, and more likely to have had a white-collar job and some postsecondary education than were nonparticipants. Difficulties of obtaining subjects and methods for avoiding these difficulties include offering many opportunities to attend and determining accurately the reason for nonparticipation.

Age Factors↗
PubMed1992

Knee extensor and knee flexor strength: cross-sectional area ratios in young and elderly men.

The relationships between isometric and isokinetic-concentric knee extensor and knee flexor strength, and quadriceps and hamstring cross-sectional area (CSA) were determined in young (n = 13, M = 24.5y) and elderly (n = 12, M = 70.7y) men. Quadriceps and hamstring CSA was determined by computed tomography. Knee extensor and flexor strength at 0 degree/s and 120 degree/s was determined on a Kin-Com isokinetic dynamometer. Compared to the young men, elderly men had significantly smaller quadriceps muscles and were weaker (22-32%) in knee flexion and knee extension at both angular velocities. Strength:CSA ratios were similar at 0 degree/s, but elderly men had decreased ratios for both extensors and flexors at 120 degree/s. Correlations of knee extensor and flexor strength with muscle CSA were significant at both velocities in elderly men, but not at either velocity for the knee flexors in young men. The decrease in isometric strength in elderly men can be accounted for by their decrease in muscle CSA, but their decrease in isokinetic-concentric strength was greater than their loss of CSA. Further study is required to determine the reason for this nonproportional loss of isokinetic-concentric strength.

Adult↗
PubMed1992

Combined papaverine test and radionuclide penile blood flow in impotence: method and preliminary results.

The investigation of vascular impotence requires a simple, reliable and non-invasive method of estimating penile arterial supply. A method for measuring flow to the dependent portion of the penis has been developed using technetium-labelled red blood cells (99mTc-RBC). Its use, in conjunction with the intracavernous injection of papaverine, was investigated in 32 patients with various causes of impotence. Intracavernous papaverine was administered and a pneumatic cuff was inflated around the base of the penis both to isolate the penile circulation and to prevent dispersion of papaverine. The remaining blood pool was labelled with 99mTc-RBC. A gamma camera was used to produce a time-activity curve for the penis following release of the cuff. Penile blood flow was calculated from the initial gradient of the time-activity curve. Papaverine-stimulated penile blood flow was significantly greater in patients without evidence of arterial insufficiency. None of the subjects with arterial disease achieved flows greater than 20 ml/min/100 ml, while flow in patients without arterial disease exceeded this value. Flow estimation without the use of papaverine was not able reliably to discriminate between the 2 groups. There was no difference in papaverine-stimulated blood flow between impotent subjects with veno-sinusoidal leakage, in the absence of arterial disease, and a control group who achieved full erection with papaverine. It was therefore possible, by assessing the response to papaverine and measuring arterial blood flow, to distinguish between arterial insufficiency, veno-sinusoidal leakage and non-vascular causes of impotence. The method requires little skill and can be modified for use with inexpensive equipment.

Adult↗
PubMed1992

Thigh composition in young and elderly men determined by computed tomography.

Computed tomography (CT) was used to quantify components of the thigh in young (n = 13) and elderly (n = 11) men. Cross-sectional areas (CSA) of the total limb, total muscle plus bone, quadriceps compartment, hamstring compartment and bone were measured at each of five scan sites along the length of the thigh. Non-muscle tissue (NMT) areas within the muscle compartments were measured using changes in density based on Hounsfield units. Skin plus subcutaneous fat areas and quadriceps and hamstring lean muscle areas were calculated by subtraction. Geometric formulae were used to calculate related volumes for each thigh component. Volumes were also predicted from regression equations employing thigh length and component CSA from single mid-limb CT scans. The results showed that while total thigh CSA was not different in elderly men, they had significantly smaller total muscle plus bone (13.0%), and quadriceps (26.4%), and hamstring (17.9%) muscle areas. The elderly men also had significantly greater CSA for skin plus subcutaneous fat (37.6%), and for NMT in the quadriceps (59.4%) and hamstring (127.3%) muscle compartments. These results suggest that comparisons of relative leg muscle strength between young and elderly men may be misleading due to the decrease in actual muscle tissue associated with ageing. Appropriate quantification of muscle size and CSA must be carried out before such comparisons can be meaningful.

Aging↗
PubMed1992

Endurance training of older men: responses to submaximal exercise.

The purpose of this study was to quantify the exercise response of older subjects on a time-to-fatigue (TTF) submaximal performance test before and after a training program. Eight older men (67.4 +/- 4.8 yr) performed two maximal treadmill tests to determine maximum oxygen uptake (VO2max) and ventilation threshold (TVE) and a constant-load submaximal exercise treadmill test that required an oxygen uptake (VO2) between TVE and VO2max. The submaximal test, performed at the same absolute work rate before and after the training program, was performed to volitional fatigue to measure endurance time. The men trained under supervision at an individualized pace representing approximately 70% of VO2max (80% maximum heart rate) for 1 h, four times per week for 9 wk. Significant increases were demonstrated for VO2max (ml.kg-1.min-1; 10.6%); maximal ventilation (VE, l/min; 11.6%), and TVE (l/min; 9.8%). Weight decreased 2.1%. Performance time on the TTF test increased by 180% (7.3 +/- 3.0 to 20.4 +/- 13.5 min). The similar end points for VO2, VE, and heart rate during the TTF and maximal treadmill tests established that the TTF test was stopped because of physiological limitations. The increase in performance time among the subjects was significantly correlated with improvements in VO2max and TVE, with the submaximal work rate representing a VO2 above TVE by 88% of the difference between TVE and VO2max pretraining and 73% of this difference on posttraining values.

Aged↗
PubMed1992

Eccentric and concentric torques of knee and elbow extension in young and older men.

The purpose of this study was to compare the strength of knee extensors and elbow extensors in young and older men under conditions of eccentric loading and concentric contractions. Twelve men ages 23 to 32 years and 12 ages 60 to 75 years were tested at two angular velocities of movement, 90 and 180 degrees.s-1, on a KinCom isokinetic dynamometer. Compared to young men, older men had lower concentric peak torque values for elbow (31%) and knee (32%) extensors (p less than 0.05). The older group showed lower eccentric peak torques on all elbow comparisons (21% lower), and for knee extension at the slower velocity (20%). At the faster velocity, knee extension eccentric peak torque did not differ from that of younger men. Differences between the age groups were significantly less for the eccentric muscle action than for the concentric one. The observation of maintained eccentric strength in older men, particularly at fast velocity, warrants research in defining the mechanism.

Adult↗
PubMed1992

The effect of interval and continuous training on the aerobic parameters.

The purpose of this study was to investigate changes in the parameters of aerobic function resulting from continuous training (CT) and interval training of both low power (LPO-IT) and high power output (HPO-IT). Untrained males (n = 17, 25.1 yrs) trained 10 weeks on cycle ergometers (four 40-min sessions a week) at 80% VO2max. Cycle ramp function tests at 0 and 10 weeks were used to determine the four aerobic parameters:VO2max, ventilation threshold (VeT), effective time constant for O2 uptake kinetics (MRT), and work efficiency (eta): VO2max increased significantly (3.30 to 3.66 l.min-1). Absolute VeT increased significantly (2.17 to 2.45 l.min-1) but there was no change in the relative threshold (VeT/VO2max). MRT decreased significantly from 38.8 to 33.1 seconds and there was no change in eta. There were no between-group differences; thus neither low power output nor high power output interval training offers an advantage over continuous training of the same average power output in altering the aerobic parameters.

Adult↗
PubMed1991

Personality. Type A behavior, and the effects of beta-blockade.

In a previous report, it was shown that a dimension of personality entitled dependence/independence could be used to distinguish the cardiovascular and catecholaminergic response to stress in type A individuals. This study is a continuation of the previous work. It examines the relative effects of beta-blockade on stress-induced changes in heart rate, blood pressure, and catecholamines in two groups of type A individuals who differ in reactivity. Sixty-six healthy, middle-aged men with type A behavior were classified as dependent (high reactivity) or independent (low reactivity). The effects of beta-blockade on the two groups were tested in a randomized, double-blind, crossover trial utilizing a mental stressor, a physical stressor, and work day monitoring. Results showed that, in comparison with the independent type As, those who had been classified as dependent had higher heart rates in all three stress conditions and had higher epinephrine levels during both the mental and physical stressors. For both groups, beta-blockade lowered the heart rate and systolic blood pressure but increased norepinephrine with the mental stressor and epinephrine and norepinephrine with the physical stressor. It also reduced the mean work day heart rate. For the dependent type As, the drug had a greater effect on increasing epinephrine during the physical stressor and by reducing the percent of the work day spent in high heart rate zones. The results are discussed from the point of view of identifying type As who may be particularly coronary prone and the potential effects of beta-blockade on the reactivity associated with type A behavior.

Adult↗
PubMed1991

Sequential renography in acute urinary tract obstruction due to stone disease.

A group of 76 patients with urographically proven acute calculus obstruction was studied prospectively using 99mTc-DTPA renography to see if kidneys at risk of irreversible renal damage could be identified. There was a statistically significant relationship between the presence of obstruction on renography and the subsequent requirement for intervention, but not with the degree of obstruction (partial or severe). Stones over 5 mm in size are highly likely to cause obstruction, a drop in relative renal function and require intervention. In all, 14 patients sustained a drop in relative renal function of greater than 7% on renography and 12 of these returned to normal limits when their calculi had been passed or removed. The 2 kidneys whose function remained impaired had fallen below 25% of overall renal function and both patients had received prior treatment for their calculi. No patient who presented de novo suffered any permanent loss of ipsilateral renal function. The results confirm that the criteria for intervention were well founded and emphasise the importance of achieving a stone-free state after primary treatment. Renography is recommended for stones over 5 mm in size, those in the middle and upper ureter and for those patients discharged with a stone in situ.

Adult↗
PubMed1991

Diagnostic value of lung clearance of 99mTc DTPA compared with other non-invasive investigations in Pneumocystis carinii pneumonia in AIDS.

Various non-invasive investigations were carried out in patients infected with HIV who had respiratory symptoms with and without pneumocystis pneumonia (with pneumonia, n = 13 (five smokers); without pneumonia, n = 22 (13 smokers]. These included chest radiography; lung function tests (forced expiratory volume in one second, forced vital capacity; transfer factor and coefficient for carbon monoxide); arterial blood gas tensions; arterial oxygen saturation at rest and on exercise; and lung clearance of diethylenetriaminepenta-acetic acid labelled with technetium-99m (99mTc DTPA). The effect of scan time (seven v 45 minutes from peak counts) and subtraction of background counts were examined. There were no significant differences between the two groups in lung function tests or arterial blood gas tensions at rest. The median clearance half time of inhaled 99mTc DTPA for the first seven minutes from peak counts was 7.2 minutes for patients with pneumocystis pneumonia and 22 minutes for those without. The median arterial oxygen desaturation on exercise was 5% in patients with pneumocystis pneumonia and 2% in those without. 99mTc DTPA lung clearance was better than the other non-invasive tests in discriminating pneumocystis pneumonia from other pulmonary disorders in patients positive for HIV. A short scan time of seven minutes was as sensitive and specific as the longer scan time of 45 minutes, and this allows the clearance of 99mTc DTPA to become a rapid screening test.

Adult↗