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Biomedical subjects

D A Cunningham

Publications and source records attributed to D A Cunningham.

At least 109 records · Page 6Linked to original sources
PubMed1990

Changes in peripheral chemoreflex sensitivity during sustained, isocapnic hypoxia.

One hypothesis concerning the origin of hypoxic ventilatory decline is that hypoxia acts centrally to depress peripheral chemoreflex loop activity. To investigate possible changes in peripheral chemoreflex loop activity during sustained, isocapnic hypoxia, the ventilatory responses to four one minute pulses of either extra hypoxia (45 Torr) or carbon dioxide (8 Torr above resting levels) were measured in man at minutes 2, 7, 12, and 17 of a 23 min isocapnic, hypoxic period (50 Torr). For hypoxia, the first pulse response (130%) was significantly greater (P less than 0.05) than the fourth response (74%). For CO2, pulse responses 2 and 3 (101 and 103%, respectively) were significantly greater (P less than 0.05) than the fourth response (91%). A central depression of peripheral chemoreflex loop activity should affect peripheral sensitivities to CO2 and hypoxia equally. Our results suggest that the peripheral sensitivity to hypoxia declined more than that to CO2, implying a peripheral chemoreceptor origin for hypoxic ventilatory decline.

Adult↗
PubMed1990

Type A behavior, personality, and sympathetic response.

This study examined, under two types of stress and during a typical workday, the moderating effects of the personality trait dependence/independence on the hemodynamic and catecholaminergic response in Type A individuals. During the mental stressor, Type As with strong dependency needs showed elevated heart rates and higher levels of epinephrine. During the physical stressor, they showed elevated heart rates and higher levels of norepinephrine. During the typical workday, both urinary catecholamines and mean daily heart rates were higher. It is suggested that these findings, which indicate greater sympathetic-adrenal response, are the result of a basic personality/behavior inconsistency and that Type A behavior may have an accentuated relationship to coronary disease when overlaid on a personality for which it is inconsistent.

Adult↗
PubMed1990

A comparison of anthropometry with computed tomography in limbs of young and aged men.

Arm and leg composition determined by anthropometry (AP, girths, and skinfolds) were compared with computed tomography (CT) in 7 young (mean age 31.4y) and 13 old (74.8y) males. Five transverse CT scans, girths, and skinfold measurements were made. In each CT image, total cross-sectional area (CSA), bone CSA, muscle compartment CSA, and "pure" muscle CSA within the compartment were measured. Corresponding volumes were also calculated. Total limb and muscle plus bone CSA and volumes were estimated from AP measures. The two methods were compared, and multiple regression analyses were used to predict component CSA and volumes from AP measures. In both groups, AP component measures in the leg provided more accurate values than in the arm. Skin plus subcutaneous tissue in the old was not well estimated by AP. The greater preponderance of nonmuscle tissue in the muscle compartments of the old, as determined from CT images, was not related to any AP estimates. Prediction equations for various component areas and volumes were derived. Some equations derived for the young could not be obtained for the old due to the reduced ability of AP to accurately assess limb composition of aged men.

Adult↗
PubMed1990

Changes in arterial K+ and ventilation during exercise in normal subjects and subjects with McArdle's syndrome.

1. We have examined the relationship between ventilation (VE), lactate (La) and arterial plasma K+ concentrations [( K+]a) during incremental exercise in six normal subjects and in four subjects with McArdle's syndrome (myophosphorylase deficiency) who do not become acidotic during exercise. 2. In normal subjects, [K+]a rose to ca 7 mM at the point of exhaustion. The time courses of the increases in VE, La and [K+]a were all similar during the exercise period. La reached its peak concentration during the recovery from exercise when both VE and [K+]a were returning to resting levels. 3. McArdle's subjects, like normal subjects, had a non-linear ventilatory response during incremental exercise. Their [K+]a was closely related to VE throughout exercise and recovery. 4. The arterial pH of McArdle's subjects, rather than remaining constant, actually rose from the onset of exercise. 5. For a given level of exercise, the levels of VE and [K+]a were greater in the McArdle's subjects than in normal subjects. 6. These findings are consistent with the idea that hyperkalaemia may contribute significantly to the drive to breathe, especially during heavy exercise.

Adult↗
PubMed1990

A comparison of indirect methods for continuous estimation of arterial PCO2 in men.

Four different measures (PETCO2, PACO2, PADCO2, and PJCO2) for indirectly estimating arterial PCO2 (PaCO2) from respired gas at the mouth have been investigated. PETCO2 was the end-tidal PCO2. PACO2 was calculated using a reconstruction of the alveolar oscillation of PCO2 obtained from the end-tidal "plateau" in PCO2. PADCO2 was calculated as for PACO2 except that the effects of dead space were incorporated. PJCO2 was calculated from an empirical relationship involving PETCO2 and tidal volume. Six subjects were studied at rest and during cycle ergometry at 50 and 100 W while breathing a variety of gas mixtures. Arterial samples were drawn for determination of true PaCO2. The differences for each method between estimated and true PaCO2 at rest and at 50 and 100 W were as follows: PETCO2, -1.35 +/- 2.64, 1.67 +/- 2.31, and 2.67 +/- 2.02 (SD) Torr; PaCO2, -2.15 +/- 2.73, -0.80 +/- 2.18, and -0.35 +/- 2.31 (SD) Torr; PADCO2, -1.55 +/- 2.54, 0.25 +/- 2.16, and 0.63 +/- 2.26 (SD) Torr; and PJCO2, -1.41 +/- 2.30, 0.12 +/- 1.79, and 0.08 +/- 1.96 (SD) Torr. It is concluded that, at rest, all methods significantly underestimate true PaCO2 and during exercise PETCO2 significantly overestimates PaCO2, but no bias was detected for any of the other methods.

Adolescent↗
PubMed1990

Effect of an exercise program on the perception of exertion in males at retirement.

To describe the association between perception of exertion and exercise, 138 men at retirement, mean age 62.7 years, were studied before and after a one-year program of exercise. VO2max and ratings of perceived exertion (RPE) using the Borg psychophysical scale were determined by a continuous exercise treadmill protocol to fatigue. The men were randomly assigned to an exercise program (n = 69) or control (n = 69). The program consisted of walking or jogging for 30 min, 3 times per week for one year. After training, the activity group showed a significant improvement in VO2max (12%). Linear regression analysis was used to relate RPE to selected physiological measurements for control and activity groups. The equations for the before and after training relationships were compared. Changes in the relationship of RPE vs VO2 and Ve, after training, were not significant for the activity group. However, the control group showed significant changes in these relationships at one year post retirement. For VO2 and Ve, ratings were 1-2 units higher than at time of retirement. Results indicate that perception of a physical task normally changes at retirement such that a given amount of exertion may seem subjectively greater. Results also suggest that a structured exercise program is successful at maintaining perception of task at pre-retirement levels. This maintenance of a low rating of perception may retard a reluctance to be physically active which often accompanies ageing.

Aged↗
PubMed1989

Comparison of twitch potentiation in the gastrocnemius of young and elderly men.

The capacity for twitch potentiation in the gastrocnemius muscle was determined following maximal voluntary contractions (MVC) in 11 elderly (means +/- SD; 66.9 +/- 5.3 years) and 12 young (25.7 +/- 3.8 years) men. Potentiation was observed by applying selective stimulation to the muscle belly, 2 s after a 5 s MVC. With this procedure, both groups showed significant (P less than 0.05) increases in twitch tension in the gastrocnemius (ratios of potentiated twitch to baseline were means = 1.68 +/- 0.40 for young vs means = 1.40 +/- 0.20 for the elderly, P less than 0.001). Time to peak tension of the twitch decreased from means = 101.5 +/- 17.9 ms to means = 88.0 +/- 15.8 ms in the young men following potentiation; the respective values for the older men were 136.7 +/- 17.9 ms and 133.1 +/- 28.6 ms. These changes resulted in a greater rate of tension development in the potentiated state. The elderly gastrocnemius thus showed qualitatively similar changes in the isometric twitch following potentiation, but reduced and prolonged responses in comparison to young adults. Slowed muscle contraction and reduced capacity for potentiation may be physiological correlates of the reported morphological changes in aged skeletal muscle.

Adult↗
PubMed1989

Clinical diagnosis from digital displays: preliminary findings of the St Mary's Evaluation Project.

Image quality is a fundamental issue in the introduction of picture archiving and communications systems (PACS), and one that has hitherto been eclipsed by other aspects of the considerable technological challenge facing scientists and manufacturers involved in its development. We conducted a formal evaluation of clinical radiological diagnosis from a commercially available PACS viewing station, using subperiosteal resorbtion in renal osteodystrophy as the test pathological diagnosis, with receiver operating characteristic (ROC) analysis of the results. We conclude that the displayed, digitised images were inferior to film using the apparatus tested and believe that careful, objective clinical evaluation of such systems is of paramount important.

Chronic Kidney Disease-Mineral and Bone Disorder↗
PubMed1989

Vascular graft infection: the role of indium scanning.

Infection of a prosthetic graft is one of the most feared complications of vascular surgery. The difficulties of accurate, objective diagnosis are well recognised. We have used III Indium labelled white blood cell scans (InWBC) in two groups: 9 control patients who underwent uncomplicated aortic aneurysm surgery, and 23 patients with suspected graft sepsis. In the control group there was one positive scan in a patient with an inflammatory aneurysm. In the suspected sepsis group, 11 patients subsequently has proven graft sepsis. Nine were correctly predicted by Indium scanning. Ten of 12 patients who did not have proven graft sepsis had negative scans. There was a total of 5 inflammatory aneurysms in the control and suspected sepsis groups, of whom two had positive scans. False positive scans were not present in the early postoperative period i patients without inflammatory aneurysms. In our experience Indium labelled WBC scanning for suspected graft sepsis has a accuracy of 83% a negative predictive value of 83% and a positive predictive value of 82%. These results suggest that Indium white cell labelling techniques which do not involve substantial cross-labelling of platelets are the best objective methods of establishing the presence or absence of graft sepsis.

Aorta↗
PubMed1989

Arm and leg composition determined by computed tomography in young and elderly men.

Five computed tomography (CT) scans were taken at measured intervals of the legs and arms of young (n = 7) and elderly (n = 13) men. Cross-sectional areas (CSA) of the total limb, muscle plus bone and bone were measured in each scan, and skin plus subcutaneous tissue areas were calculated by subtraction. In addition, in the arm scans the CSA of the extensor and flexor compartments were measured, and in the leg the CSA of the plantar flexor compartment. A value for lean muscle within these compartments was calculated by excluding non-muscle tissue using density measurements based on Hounsfield units. Related volumes for the various components were also calculated using geometric formulae. The results showed that elderly limbs were of a similar overall size as the young, but elderly muscles were smaller (28-36%) with greater amounts of non-muscle tissue located within a muscle, particularly in the plantar flexors (81% more than in the young). Elderly arms had a greater amount of skin plus subcutaneous tissue than the young, but there was no difference in the legs. Muscle volumes were similar to in vitro results reported from cadaver studies and can be predicted from single mid-limb CT scans using regression equations. These results illustrate that, due to the substantially reduced amount of 'pure' muscle tissue in the elderly, comparisons of relative strength with other populations may be misleading unless appropriate measurements of muscle size are considered. Methods to estimate in vivo physiological CSA, which is considered the best means of normalizing strength, have been demonstrated in this study.

Adult↗
PubMed1989

The self-selected walking pace test and beta blockade.

The self-selected walking pace test is a safe, simple and inexpensive test to measure an individual's perception of walking speed and is more strongly related to maximal oxygen uptake than to age. This study was carried out to determine whether beta blockade, which commonly causes fatigue, would affect the test. Twenty-three clinically healthy men with a mean age of 43 years completed the test both on and off 80 mg long-acting oxprenolol daily, a beta blocking drug with partial agonist activity. The men walked 80 m at three self-selected speeds (rather slow, normal and rather fast). There was a significant reduction in heart rate on the drug. The walking speed at the three paces on and off medication were 1.08 ms-1 and 1.07 ms-1 (slow), 1.32 ms-1 and 1.33 ms-1 (normal) and 1.63 ms-1 and 1.61 ms-1 (fast). None of these differences reached statistical significance. The stride length also did not change. It is concluded that beta blocking medication does not interfere with the self-selected walking pace test.

Adrenergic beta-Antagonists↗
PubMed1989

Influence of age and physical training on postural adaptation.

Movement from the supine to the upright position brings about the transfer of blood from the upper to the lower body. Cardiac output and central arterial pressures are reduced causing, in the normal subject, a reflex increase in sympathetic and a decrease in parasympathetic activity. Increased sympathetic activity facilitates cardiovascular and skeletal muscular adjustments aimed at maintaining cerebral blood flow. If there were no compensatory cardiovascular changes, the reduced cardiac output due to the pooling of blood into the dependent regions of the body would result in cerebral ischemia and loss of consciousness (postural hypotension). This situation is most often experienced in the elderly population and can have quite a debilitating influence on daily living activities. It is known that as humans age, the efficiency of bodily functions often becomes impaired. It is also known that exercise can improve the function of the cardiovascular system as shown by an improved work capacity and lowered incidence of heart disease and high blood pressure. These exercise-related changes suggest that exercise may have implications in the management of postural hypotension. However, recent studies have given conflicting accounts regarding the relationship between regular exercise and postural adaptation, with some studies describing an impaired adaptation in athletes. The purpose of this paper is to summarize, in detail, the influences of age and physical fitness on postural adaptation.

Adaptation, Physiological↗
PubMed1989

Strength in an elderly population.

Strengths of several upper- and lower-limb muscle groups were measured in an elderly population by using a simple, adaptable dynamometer. The bladder of a sphygmomanometer was modified by folding and surrounding it in a sewn cloth bag. It was then attached to a board for improved stability during the tests. Thirty-seven men and 81 women aged 62 to 102 years were tested. Four muscle groups were statistically determined to best represent strength-two for upper limb and two for lower limb. These strength measures were correlated with anthropometric indices, and a step-wise multiple regression was used to determine the degree of association between the variables. Men were significantly stronger than women in absolute strength, but were not different when strength was expressed relative to body weight. Within each sex, however, age was the most important variable related to loss of strength; body weight was secondary or not significant. These results suggest that age is the most important factor for relating differences in strength in an older elderly population (those aged 75 to 90 or more years). This factor must be accounted for just as body weight or cross-sectional muscle area often are, when comparing strengths in a younger population.

Aged↗
PubMed1988

Comparison of the histochemical and contractile properties of human triceps surae.

Contractile and histochemical properties of the triceps surae were compared in 16 males and 4 females aged 20 to 49 years. Surface electrical stimulation was used to determine twitch, tetanic and fatigue parameters. From these tests, twitch tension (Pt), time to peak tension (TPT), half relaxation time (1/2 RT), tetanic tensions at 10, 20 and 50 Hz and an index of fatigue (FI) were calculated. A maximal voluntary contraction (MVC) was also performed. Muscle samples from the belly of the lateral gastrocnemius were obtained using the needle biopsy technique. The samples were treated histochemically for myosin ATPase and NADH-tetrazolium reductase in order to classify the fibres as either Type I, slow twitch (ST) or Type II, fast twitch (FT) and to determine fibre areas. Correlations were performed between the grouped male and female contractile and histochemical variables. The results demonstrated significant positive relationships demonstrated significant positive relationships between percentage of ST fibres (%ST) and TPT (r = 0.49), and %ST and the ratio of tetanic forces at 10 Hz to 50 Hz (Po10/Po50) (r = 0.55). No significant relationships were obtained for Pt, 1/2 RT, MVC or FI with any histochemical parameter. The results suggest that fibre type distribution determined using myosin ATPase is related to electrically stimulated isometric contractile speeds and not to voluntary force generation (MVC) or electrically induced fatigue.

Adult↗
PubMed1988

Fatigue and recovery contractile properties of young and elderly men.

The 24 h recovery pattern of contractile properties of the triceps surae muscle, following a period of muscle fatigue, was compared in physically active young (25 years, n = 10) and elderly (66 years, n = 7) men. The fatigue test protocol consisted of 10 min of intermittent submaximal 20 Hz tetani. The maximal twitch (Pt) and tetanic force at 3 frequencies (10, 20 and 50 Hz) were determined at baseline and at 15 min, 1, 4 and 24 h after fatiguing the muscle. Maximal voluntary contraction (MVC) and vertical jump (MVJ) were also assessed. The loss of force during the fatigue test was not significantly different between the young (18 +/- 13%) and elderly (22 +/- 15%). Both groups showed similar and significant reductions of Pt (15%), tetanic force (10 to 35%) and rate of force development (dp/dt) (20%) 15 min and 1 h into recovery. The loss of force was greater at the lower stimulation frequencies of 10 and 20 Hz. Time-to-peak tension was unchanged from baseline during recovery in either group. The average rate of relaxation of twitch force (-dPt/dt) was decreased (p less than 0.05) and half-relaxation time significantly increased at 15 min and 1 h in the elderly but not the young. The findings indicate that after fatiguing contractions, elderly muscle demonstrates a slower return to resting levels of the rate and time course of twitch relaxation compared to the young.

Adult↗
PubMed1988

Comparison of cardiovascular response to passive tilt in young and elderly men.

To test the hypothesis that altered hemodynamic responses to postural changes are associated with aging, cardiovascular responses to head-up tilt (HUT) and head-down tilt (HDT) were examined in 12 healthy young (average age, 24.6 +/- 1.7 years) and 12 healthy elderly (average age, 68.6 +/- 2.2 years) men. Subjects were passively tilted from supine to 30 degrees, 60 degrees, and 90 degrees HUT and HDT. Responses to these perturbations were determined 5 min after tilting with measures of heart rate (HR), blood pressure (SBP, DBP), and echocardiographically determined left ventricular diameter in systole and diastole (LVIDs, LVIDd). In HUT there were no significant age effects. In both young and elderly, SBP decreased significantly (p less than 0.05), and DBP and HR increased significantly. Ejection fraction (EF), mean arterial blood pressure (MABP), and rate-pressure product (RPP) were unchanged in both groups. In HDT, the hemodynamic responses of the young and elderly were in opposite directions and significant age effects were found for SBP, DBP, HR, LVIDs, EF, MABP, and RPP. In HDT, the young appear to increase cardiac output primarily due to an increase in EF and end-diastolic volume (LVIDd), while HR is unchanged and SBP is decreased. MABP is unchanged, suggesting a small decrease in total peripheral resistance. The elderly may increase cardiac output slightly, owing to an increase in LVIDd with no change in EF, and a large increase in HR. Afterload increased markedly, therefore attenuating any increase in cardiac output.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗