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Biomedical subjects

D R Pendergast

Publications and source records attributed to D R Pendergast.

68 records · Page 4Linked to original sources
PubMed1985

Cardiac output and muscle blood flow in exercising dogs.

Average blood flow (q) was determined by trapping of 15 micron radioactive microspheres in the vastus lateralis, the gastrocnemius-flexor digitorum superficialis and the triceps brachii of five 18 kg untrained mongrel dogs at rest and during graded treadmill running. Oxygen uptake (VO2) and cardiac output (Qco) were simultaneously determined. q leveled off in all investigated muscles at 60-100 ml X 100 g-1 X min-1 when VO2 was ca. 70% of peak VO2. Qco increased linearly with VO2 up to peak VO2. The regional blood flow (qR) distribution pattern within the muscle was found to be extremely scattered around q, both at rest and at heavy exercise. qR ranged from approximately 5 to approximately 55 ml X 100 g-1 X min-1 at rest and from approximately 10 to approximately 200 ml X 100 g-1 X min-1 at maximal exercise. No significant topographic pattern was observed in the qR distribution of the gastrocnemius muscle which was essentially similar to that previously found for the isolated-perfused muscle preparation. The results indicate that maximal limb muscle blood flow and/or its uneven distribution may be the primary limiting factor to peak VO2 in untrained running dogs.

Animals↗
PubMed1985

Blood flow distribution in dog gastrocnemius muscle at rest and during stimulation.

The distribution of blood flow within the isolated perfused dog gastrocnemius muscle (weight 100-240 g) was studied by intra-arterial injection of radioactively labeled microspheres (diameter 15 micron) at rest and during supramaximal stimulation to rhythmic isotonic tetanic contractions of varied frequency against varied loads. After the experiment the muscle was cut into 180-250 pieces of approximately 0.75 g each, and the blood flow to each muscle piece was determined from its radioactivity. The inhomogeneity of blood flow was represented as the frequency distribution of the ratios of regional specific blood flow, i.e., blood flow per unit tissue weight of the piece, QR, to the overall specific blood flow of the muscle, Q. The QR/Q values for the individual pieces of a muscle were found to vary widely both at rest and during stimulation. With rising work load the frequency distribution had a tendency to broaden and flatten, indicating increasing perfusion inhomogeneity. On the average of the experiments, there was no significant difference in specific blood flow between the three anatomic components of the gastrocnemius (lateral and medial heads of gastrocnemius and flexor digitorum superficialis) nor between the superficial and deep portions within these anatomic components, only the distal third of the muscle was relatively less perfused compared with the proximal two-thirds. The considerable inhomogeneity of blood flow as revealed by microsphere embolization and by other methods is expected to exert important limiting effects on local O2 supply, particularly during exercise. Its neglect would lead to serious errors in the analysis of O2 supply to muscle tissue.

Animals↗
PubMed1984

Decrease in body insulation with exercise in cool water.

Steady-state body insulation was measured in 7 healthy male subjects during rest and exercise for 3 h in water of 28 degrees C - 32 degrees C. At rest, maximal body insulation increased as a linear function of mean subcutaneous fat thickness by an amount approximately 4-fold what would be predicted from the physical insulation of fat alone. With arm plus leg exercise, body insulation declined as an exponential function of the exercise intensity, reaching approximately 25% of the resting value at work loads above VO2 = 1.2 liters.min-1. During exercise the relationship between overall body insulation and mean subcutaneous fat thickness was almost identical to that predicted from fat insulation and mean subcutaneous fat thickness was almost identical to that predicted from fat insulation alone. These results suggest that 75% of maximal body insulation in resting subjects is achieved by use of skeletal muscle as an insulative barrier and that the muscle component is increased with increasing fat thickness. This muscle insulation shell is lost during exercise. As a practical consequence, heat generated by muscular exercise in water colder than critical water temperature cannot offset cooling unless the exercise intensity is great.

Adipose Tissue↗
PubMed1984

Cardiovascular and renal responses to head-out water immersion in canine model.

Water immersion (WI) of anesthetized dogs to the midcervical level in the vertical sitting position under thermoneutral conditions (38 degrees C) leads to generalized increases in regional blood flows (radiolabeled microspheres) to most tissues. The increased flows can be accounted for by increased local VO2 in some tissues (heart, respiratory muscle), or by local heating (skin, fat). However, an alteration in the relation between cardiac output (Q) and VO2 appears to play a role in the large flow increments observed in skeletal muscle and abdominal viscera in WT. Studies of conscious, chronically instrumented dogs during 100 min of thermoneutral WI at 37 degrees C in the quadruped position indicate that both left atrial and aortic transmural distending pressures and left ventricular contractile performance (LV dP/dtmax) increase, while total peripheral resistance is unchanged. Cardiac output increases largely in association with an increase of heart rate. In addition, urine flow, sodium excretion, and osmolal clearance all increased. The cardiovascular adjustments occurred more rapidly than the renal responses. These results indicate that the conscious dog may be useful for investigation of physiological mechanisms involved in the WI response.

Abdomen↗
PubMed1983

Sinoaortic contribution to ventilatory control in exercising dogs.

The role of the sinoaortic reflexes in the regulation of ventilation during exercise was evaluated in seven awake dogs prepared with chronic tracheostomies and arterial catheters. Each dog ran on a treadmill at several work loads before and after sinoaortic denervation and served as its own control. Minute ventilation in the sinoaortic denervated state was significantly reduced from intact values by 10-40% at the mild and moderate levels of exercise [O2 uptake (VO2) = 30-50 ml . kg-1 . min-1] mainly as a result of a lowering respiratory frequency. At higher work loads (VO2 = 70-80 ml . kg-1 . min-1) minute ventilation was similar in the intact and denervated states, but the pattern of ventilation was altered with a higher frequency and a lower tidal volume in the denervated state. The rise in ventilation toward a stable plateau was slower at all work loads in the denervated than in the intact state. After sinoaortic denervation, arterial PCO2(PaCO2) levels were significantly elevated above intact PaCO2 levels during both the preexercise period and the steady state at all exercise levels. These results suggest that the sinoaortic reflexes contribute to both the control of ventilation and the pattern of breathing during mild and heavy levels of exercise in the conscious dog.

Animals↗
PubMed1982

Regional circulatory responses to head-out water immersion in anesthetized dog.

Thermoneutral head-out water immersion (WI) of humans leads to a sustained elevation of cardiac output (QCO), while systemic VO2 is unchanged. However, the regional blood flow responses (Qr) to WI are largely unknown. In eight dogs anesthetized with pentobarbital sodium, relative to the control vertical position in air with the chest and abdomen upright (Erect1), after 30 min of WI at 38 degrees C the QCO (thermodilution), stroke volume, and aortic pressure were elevated (P less than 0.01) by 88.5 +/- 6.4% (SE), 55 +/- 9%, and 29 +/- 4% from levels of 2.24 +/- 0.01 1 X min-1, 18.4 ml +/- 1.7, and 109 +/- 7.9 mmHg, respectively. Qr (ml X min-1 X 100 g-1), measured by 15 microns-radiolabeled microspheres at WI30 min relative to the Erect1 levels, increased (P less than 0.01) in the stomach (104 +/- 27%), jejunum (78 +/- 19%), ileum (102 +/- 23%), liver (hepatic artery) (485 +/- 46%), pancreas (200 +/- 44%), spleen (88.7 +/- 33%), renal cortex (88 +/- 30%), left ventricle (157 +/- 15%), skin (726 +/- 30%), fat (680 +/- 43%), gastrocnemius (200 +/- 36%), triceps (414 +/- 61%), intercostals (317 +/- 44%), and diaphragm (477 +/- 24%). Qr responses at WI10 min were largely similar. Rectal temperature and VO2 were unchanged during WI. In the lateral recumbent position in air, QCO rose by 44.3% (P less than 0.01), but only hepatic arterial Q rose significantly (89 +/- 29%). Therefore, there may be a partial uncoupling of the normal Q/VO2 relationship in WI.

Abdomen↗
PubMed1981

Control of ventilation during graded exercise in the dog.

We analyzed the time courses of the VE, VT, and f responses to graded levels of exercise produced by increases in treadmill speed at preset inclines in 207 experiments on 15 tracheostomized dogs. At the onset of work, VE increased within 1-2 respiratory cycles (VE fast), and then either remained constant, or decreased. Following this time delay (TD), VE rose more slowly (VE slow) to attain a stable plateau (Dejours). The amplitude of VE fast, VT, and f during the TD were independent of the work load. However, the duration of the TD and the amplitude of the component mediating VE slow were workload dependent. The VE fast and the VE during the TD are the major components of the total VE response at low work levels (VO2 = 30-40 ml . min-1 . kg-1) and are mediated primarily by increased f, whereas, at higher VO2 (70-90 ml . min-1 . kg-1), VE slow is mediated largely by increased VT and this component is engaged earlier to make a greater contribution to the total VE response. In the conscious dog, the total VE response to exercise appears to be comprised of both neural and humoral components when thermal stress is minimal.

Animals↗
PubMed1979

Relationships of stroke rate, distance per stroke, and velocity in competitive swimming.

Competitive swimmers were asked to swim at a constant velocity (v) for short distances. They wore a collar to which was attached a fine non-elastic steel wire. The wire passed over two wheels of a device attached to one end of the pool. One wheel generated an impulse for every cm of forward movement and another wheel produced an electrical signal which was directly proportional to V. Measurements of distance and time were begun at definable points in the stroke cycle and were discontinued at the end of a predetermined number of strokes. In all of the four competitive strokes, front and back crawl, butterfly, and breaststroke, the V increased as a result of increasing the stroke rate (S) and decreasing the distance per stroke (d/s). In the front crawl, the male and female swimmers who achieved the fastest V had the longest d/S at slow S. The faster male swimmers also had greater percent decrease of the d/S at their maximal V than did the less skilled persons. The back crawl was similar to the front crawl except that maximal S and V were less. Increases of V of the butterfly were related almost entirely to increases in S. Except at the highest V, d/S was decreased somewhat. In the breaststroke increased V was also associated with increasing S, but the d/S decreased much more than in the other stroke styles. Fluctuations of velocity during the stroke cycle were least in the front and back crawl (+/- 15--20%) and greatest in the butterfly and breaststroke (+ 45--50%). The results were compared to the S observed and the values for V and d/S calculated for a large group of swimmers competing in the 1976 U.S. Olympic Trials. The implications of the findings for coaching swimmers are discussed.

Biomechanical Phenomena↗
PubMed1977

Quantitative analysis of the front crawl in men and women.

Body drag, D, and the overall mechanical efficiency of swimming, e, were measured from the relationship between extra oxygen consumption and extra drag loads in 42 male and 22 female competitive swimmers using the front crawl at speeds ranging from 0.4 to 1.2 m/s. D increased from 3.4 (1.9) kg at 0.5 m/s to 8.2 (7.0) kg at 1.2 m/s, with D of women (in brackets) being significantly less (P less than 0.05) than that of men. Mechanical efficiency increased from 2.9% at 0.5 m/s to 7.4% at 1.2 m/s for men, the values for women being somewhat greater than those for men. The ratio, D/e was shown to be identical to the directly measured energy cost of swimming one unit distance, V02/d, and was independent of the velocity up to 1.2 m/s. It averaged 52 and 37 l/km for men and women respectively (P less than 0.05). When corrected for body surface area the values were 27 and 22 l/km-m2 for men and women, respectively (P less than 0.05). The underwater torque, T, a measure of the tendency of the feet to sink, was 1.44 kg-m for men and 0.70 kg-m for women (P less than 0.05). VO2/d increased linearly with T for both men and women of similar competitive experience. However, the proportionality constant delta VO2/d-delta T was significantly less for competitive than noncompetitive swimmers. The analysis of the relationship VO2/d vs. T provides a valuable approach to the understanding of the energetics of swimming.

Adolescent↗
PubMedDate not supplied

Muscle fiber composition and length-tension relationships in rats chronically exposed to alcohol.

Adult Fischer 344 rats were fed an alcohol diet (7-9 g/kg/day) for 12 weeks and were compared to pair-fed controls with regard to the contraction and fiber characteristics of the gastrocnemius and plantaris muscles of the leg. Muscles were isolated in situ with blood and nerve supplies intact. The muscles were stretched by 1 mm increments and were stimulated at each muscle length with a voltage (1 msec pulse) that had been observed to produce maximal twitch force at the initial muscle length. Maximal twitch tension was found to be only 10% less in alcohol than pair-fed rats and the increase in force resulting from stretching was approximately 15% less in alcohol than pair-fed rats. No significant changes in sciatic nerve conduction velocities were produced by alcohol exposure. Moreover, no significant differences in muscle weight or the number and size of Type I, Type IIa or Type IIb muscle fibers were observed. Although the 12 weeks of alcohol exposure affected muscle physiology and histology in the direction of increased impairment, the differences were not large enough to be statistically significant.

Alcoholism↗
PubMedDate not supplied

A survey of muscle function in detoxified alcoholics.

Selected characteristics of arm and leg muscle contraction were examined in a racially mixed group of male detoxified alcoholics (N = 45, ages 20-49) and age-matched controls (N = 75). Lifetime drinking histories estimated the mean lifetime consumption of ethanol to be 8.96, 12.1 and 20.4 kg ethanol/kg body weight for alcoholic subjects aged 20-29, 30-39 and 40-49, respectively. The severity of the alcohol dependence syndrome (ADS scale) was marked in alcoholics, but was not age-dependent. Alcoholics did not differ significantly from controls on health status or physical activity scales. The performance of alcoholic subjects was impaired on all muscle function measures, with relatively more impairment found in older alcoholics. Maximal knee extension force generated at 3 muscle lengths (hip, angle, 45 degrees, 90 degrees, 180 degrees) was impaired only in alcoholics 30-49 years of age. Forearm (handgrip) muscle strength was impaired in all age groups of alcoholics. Maximal muscle (biceps) contraction speed at 3 levels of resistance was impaired only in alcoholics in their fifth decade of life. The greatest deficit in alcoholics (all age groups) was observed in the anaerobic power (bicycle ergometer) test. Thus, the magnitude of dysfunction and the extent of age-relatedness was found to be a function of the muscle test employed.

Adult↗
PubMedDate not supplied

An exponential model of isometric muscular fatigue as a function of age and muscle groups.

Despite the recommendations that an important design criterion is not to exceed 15% of an operator's maximum voluntary contraction (MVC) with any muscle that must be used for a long period of time, many tasks involve the exertion of much higher forces coupled with long-term contractions. Many studies have investigated the force-time relationship of isometric muscle contractions to determine the endurance time of a given relative force. To date, however, direct studies of muscle performance throughout fatiguing tasks have not been conducted to the same degree. This research was concerned with studying the effects of different muscle groups (biceps vs quadriceps) of subjects with different age groups (20-29 vs 50-59 years of age) on long-term muscular isometric contractions at different levels of %MVC (20%, 40%, 60%, 80%, and 100% MVC), and modelling the functional data to describe the time course of strength decrement. The data revealed that the time course of strength decrement was best modelled by the function: [formula: see text] An experiment, using 20 subjects with each subject performing 10 conditions (two muscle groups x five levels of %MVC), showed that this function accounted for over 95% of the variance of strength decrement. All parameter estimates were statistically significant.

Adult↗
PubMedDate not supplied

Quantitative evaluation of a home exercise program on muscle and functional capacity of patients with osteoarthritis.

Rehabilitation of patients with osteoarthritis of the knees is typically based on home exercise. These programs are believed to benefit patients and have been shown to qualitatively improve strength. The purpose of the present study was to quantify the effects of a 3-mo home exercise program on muscle function and functional capacity. The progressive program included flexibility, strength, endurance, active range of motion and functional activities. Nineteen subjects (67.4 +/- 7.5 yr) with osteoarthritis of the knees began the program, with only nine completing it. The subjects initially had significantly reduced muscle function and functional capacity. Maximal isometric strength of knee extension increased significantly at a knee flexion position of 45 degrees for hip flexion positions of 120 degrees and 60 degrees (35%); however, it failed to increase at longer muscle lengths. There were no significant improvements in hamstring strength. Maximal angular velocity improved after 3 mo of exercise (40%). Muscle endurance did not improve significantly. Although there was a slight increase in functional capacity, these data failed to demonstrate significant clinical or statistical improvement in overall function in patients after home exercise.

Aged↗