Biomedical subjects

G G Rogers

Publications and source records attributed to G G Rogers.

At least 19 recordsLinked to original sources

PubMed2005

Visual evoked potentials, reaction times and eye dominance in cricketers.

AIM: Few studies have examined the physiology of cricket, including the difference in ability between batsmen to make controlled contact with a ball bowled at high speed. METHODS: We therefore measured visual evoked potentials and choice reaction times with dominant eyes, non-dominant eyes, and both eyes together, in 15 elite batsmen and 10 elite bowlers (aged 20.9 SD 1.9 years) and 9 control subjects (aged 20.2 SD 1.5 years). The latency and amplitude of waves N70, P100 and N145 were determined for each visual evoked potential (VEP). In addition interpeak latencies and peak to peak amplitudes were measured. The subjects also completed a choice reaction test to a visual stimulus. RESULTS: We found that cricketers were not more likely to have crossed dominance (dominant eye contralateral to dominant hand) than controls. Cricketers had a faster latency for VEP wave N70 than controls (p=0.03). However reaction time was not different between cricketers and the control group. Across all subjects, in comparison to monocular testing, binocular testing led to a faster choice reaction time (p=0.02) and larger amplitudes of VEP wave N70 (p=0.01). CONCLUSION: Visual processing during the first 100(-1)50 ms of the balls flight together with binocular vision facilitates retinal activation in talented cricketers.

Adult↗

PubMed2005

Determinants of ball release speed in schoolboy fast-medium bowlers in cricket.

AIM: Studies investigating determinants of ball release speed have examined the technique and anthropometry of fast bowlers with little work being done on muscular strength. The aim of our study was to determine whether knee biomechanics during bowling and strength of the shoulder and knee could predict ball release speed. METHODS: Twelve cricketers, aged 16.6+/-0.7) years, from schools in Johannesburg, South Africa, volunteered for the study. Subjects were fast-medium bowlers (mean ball release speed of 29.2+/-1.8 m.s(-1)) and had been bowling for at least 5 years. Three accurate deliveries were filmed on an outdoor cricket pitch, in the sagittal plane with a high-speed digital camera recording at 250 frames per second. The mean ball release speed, knee angle at ball release and knee angle at front foot strike were determined using simple two-dimensional kinematics. On a separate day, peak concentric isokinetic muscle torque was measured for both knees and the dominant shoulder. RESULTS: Ball release speed was positively correlated to a straight knee at front foot strike (r=0.72, P=0.009) and at ball release (r=0.71, P=0.011). No significant correlation was found between ball release speed and any of the peak torque values (knee extension peak torque, r=-0.11, knee flexion peak torque, r=-0.08, shoulder internal rotation peak torque, r=0.21 and shoulder external rotation, r=0.29, P>0.05). A multiple regression model using knee angle at front foot strike and at ball release, and the angle at which peak torque is generated during shoulder internal and external rotation, predicted ball release speed (adjusted r2=0.85, P<0.002). CONCLUSIONS: We have confirmed that the angle of the front knee at the beginning and end of a delivery is an important correlate of ball release speed in schoolboy fast-medium bowlers. In addition we have also demonstrated that a multiple regression model based on knee kinematics and shoulder peak torque angles can be used to predict ball release speed.

Adolescent↗

PubMed2000

Primate pleuroesophageal tissue barrier frequency response and esophageal pressure waveform bandwidth in health and acute lung injury.

BACKGROUND: Dynamic intraesophageal pressure (Pes) is used to estimate intrapleural pressure (Ppl) to calculate lung compliance and resistance. This study investigated the nonhuman primate Ppl-Pes tissue barrier frequency response and the dynamic response requirements of Pes manometers. METHODS: In healthy monkeys and monkeys with acute lung injury undergoing ventilation, simultaneous Ppl and Pes were measured directly to determine the Ppl-Pes tissue barrier amplitude frequency response, using the swept-sine wave technique. The bandwidths of physiologic Pes waveforms acquired during conventional mechanical ventilation were calculated using digital low-pass signal filtering. RESULTS: The Ppl-Pes tissue barrier is amplitude-uniform within the bandwidth of conventional Pes waveforms in healthy and acute lung injury lungs, and does not significantly attenuate Ppl-Pes signal transmission between 1 and 40 Hz. At Pes frequencies higher than conventional clinical regions of interest the Ppl-Pes barrier resonates significantly, is pressure amplitude dependent at low-pressure offsets, and is significantly altered by acute lung injury. Allowing for 5% or less Pes waveform error, the maximum Pes bandwidths during conventional ventilation were 1.9 Hz and 3.4 Hz for physiologic and extreme-case waveforms in healthy lungs and 4.6 Hz and 8.5 Hz during acute lung injury. CONCLUSIONS: In monkeys, the Ppl-Pes tissue barrier has a frequency response suitable for Ppl estimation during low-frequency mechanical ventilation, and Pes manometers should have a minimum uniform frequency response up to 8.5 Hz. However, the Ppl-Pes tissue barrier adversely affects the accurate estimation of dynamic Ppl at high frequencies, with varied airway pressure amplitudes and offsets, such as the Ppl encountered during high-frequency oscillatory ventilation.

Acute Disease↗

PubMed1999

Acute appetite reduction associated with an increased frequency of eating in obese males.

OBJECTIVE: To investigate the effects of altered feeding frequencies on the relationship between perceived hunger and subsequent food intake and appetite control in obese men. DESIGN: Obese men reported in a fasted state in the morning to the laboratory where an isoenergetic pre-load (4100+/-234 kJ, which was 33% average daily energy requirement (ADER) of each subject) comprising 70% carbohydrate, 15% protein, and 15% fat was given. This was administered either as a SINGLE meal, or divided evenly over 5 meals given hourly as a MULTI feeding pattern. Five hours after the first pre-load, an ad libitum test meal was given to determine whether there was a difference in the amount of energy that was consumed between the two eating patterns. SUBJECTS: Seven non-diabetic, non-smoking, unrestrained obese men (age 37.4+/-18.5; BMI 40.02+/-10. 93 kg/m-2) were recruited for this study. Subjects were not told the precise reasons for this study but rather were informed that changes in blood glucose, insulin and free fatty acids with meal frequency were to be monitored. MEASUREMENTS: Blood glucose, serum insulin and free fatty acid (FFA) concentrations, and visual analogue scales (VAS) were measured prior to commencing the feeding regime and thereafter hourly for 5 h. Thereafter an ad libitum meal was given. The weight (and energy content) of the food consumed, and the time taken to eat lunch were recorded. Following this ad libitum lunch, the same variables were determined again (15, 45, and 75 min post-test meal). RESULTS: When given a SINGLE pre-load, 27% more (t=2.651; P<0.05) energy was consumed in the ad libitum test meal (5261+/-1289 kJ) compared to that eaten after the MULTI pre-load (3763+/-1986 kJ). This increase in food intake occurred despite no significant change in subjective hunger ratings. Over the 315 min pre-load period, peak insulin concentrations were significantly higher (F6,72=7.95, P<0.01) on the SINGLE treatment (171.2+/-129.8 microU ml-1) than on the MULTI treatment (133.7+/-70.2 microU ml-1). Serum insulin remained elevated for longer on the MULTI meal treatment, resulting in no difference in the area under the insulin curves between the two feeding treatments. There was a positive correlation (r=0.87) between the amount of energy consumed at lunch and insulin concentration before lunch in the SINGLE group. However, this relationship was not apparent when subjects were given the MULTI meal preload. CONCLUSION: Obese males fed an isoenergetic pre-load sub-divided into a multi-meal plan consumed 27% less at a subsequent ad libitum test meal than did the same men when given the pre-load as a single meal. Prolonged but attenuated increases in serum insulin concentration on the multi-meal programme may facilitate this acute reduction in appetite.

Adult↗

PubMed1999

High nocturnal body temperatures and disturbed sleep in women with primary dysmenorrhea.

Primary dysmenorrhea is characterized by painful uterine cramps, near and during menstruation, that have an impact on personal life and productivity. The effect on sleep of this recurring pain has not been established. We compared sleep, nocturnal body temperatures, and hormone profiles during the menstrual cycle of 10 young women who suffered from primary dysmenorrhea, without any menstrual-associated mood disturbances, and 8 women who had normal menstrual cycles. Dysmenorrheic pain significantly decreased subjective sleep quality, sleep efficiency, and rapid eye movement (REM) sleep but not slow wave sleep (SWS), compared with pain-free phases of the menstrual cycle and compared with the controls. Even before menstruation, in the absence of pain, the women with dysmenorrhea had different sleep patterns, nocturnal body temperatures, and hormone levels compared with the controls. In the mid-follicular, mid-luteal, and menstrual phases, the dysmenorrheics had elevated morning estrogen concentrations, higher mean in-bed temperatures, and less REM sleep compared with the controls, as well as higher luteal phase prolactin levels. Both groups of women had less REM sleep when their body temperatures were high during the luteal and menstrual phases, implying that REM sleep is sensitive to elevated body temperatures. We have shown that dysmenorrhea is not only a disorder of menstruation but is manifest throughout the menstrual cycle. Furthermore, dysmenorrheic pain disturbs sleep, which may exacerbate the effect of the pain on daytime functioning.

Adult↗

PubMed1998

The absence of a triphasic renovascular response by the multicalyceal kidney of the primate in reaction to acute, complete, unilateral, ureteric obstruction.

The early renovascular response by the ipsilateral kidney to acute, total, unilateral, ureteric obstruction was investigated in the adult male chacma baboon (Papio ursinus). Complete occlusion was effected by ligating the ureter at the brim of the bony pelvis ("N"=10). Sham studies were enacted using the same method but the ureter was not obstructed ("N"=11). Haemodynamic reactions were monitored for 12 hours. Compared with the sham-occluded set, the renal pelvic pressures in the obstructed group were significantly increased (P<0.05) from the second hour of the inquiry. However, there were no significant differences in renal blood flow, either between or within the respective cohorts. In this study, the renovascular response to acute ureteric occlusion was similar to that displayed by the multicalyceal kidney of other species under identical conditions. This reaction was fundamentally different to that exhibited by the unicalyceal kidney under similar circumstances.

Acute Disease↗

PubMed1997

Correctly selecting a liquid-filled nasogastric infant feeding catheter to measure intraesophageal pressure.

Polyvinyl chloride (PVC) nasogastric feeding catheters are used clinically to measure intraesophageal pressure as an estimate of pleural pressure for calculating lung compliance in infants. The accuracy of pressure measurement of 4 French gauge (FG) catheter sizes and three brands of liquid-filled catheter manometer systems (CMS) was evaluated by determining their resonance-frequency amplitude and phase properties. All CMS were underdamped and resonated. No CMS exhibited a uniform mean frequency response above 11 Hz. The maximum respiratory rate (Frr) within which CMS could potentially measure dynamic intraesophageal pressure within a 5% error limit was determined (Frr): the highest mean Frr recorded reliably in large-diameter catheters was 82 breaths/min. Significant CMS differences in accuracy existed between catheter FG sizes and between catheters of similar diameters but differing brands. Correlation (r2) between catheter inner diameter and CMS Frr was 0.66 across brands. In conclusion, intraesophageal PVC liquid-filled feeding catheters are suitable for estimating pleural pressures in subjects mechanically ventilated without sharp inspiratory waveforms or high respiratory rates. Quantitative frequency response characterization of different nasogastric catheter brands and different diameters is mandatory prior to their utilization.

Age Factors↗

PubMed1997

Frequency responses of infant air-balloon versus liquid-filled catheters for intra-esophageal pressure measurement.

Amplitude and phase frequency response characteristics of infant air-balloon catheters (IABC) of differing French gauge (FG) sizes and brands were quantified to determine their suitability for measuring dynamic intra-esophageal pressure (Pes) accurately. Frequency response performances of matching IABC and water-filled catheters (WFC) were also compared using the swept sine wave technique. The maximum respiratory rate within which IABCs could potentially measure Pes within a 5% error limit was calculated (FRR). Frequency responses of IABCs greater than FG size 5 exhibited underdamped resonant properties, while smaller FG size IABCs exhibited near-critical damping or overdamping. IABCs maintained uniform amplitude frequency responses up to 25 Hz, demonstrating the ability to measure Pes potentially up to 148 breaths/min within a 5% error limit. The frequency response performance of FG size 6 IABCs was similar to that of FG size 10 IABCs. Compared with matching WFCs, the frequency response performance of IABCs was significantly superior, the frequency response variability within IABC samples was lower, and IABC correlation between FG size and FRR was advantageously lower than for WFCs. FRR values for differing IABC brands and FG sizes are presented. We conclude that IABCs manufactured to infant-appropriate balloon specifications exhibit significantly superior frequency response characteristics compared with matching WFCs. Measurement accuracy is not improved using IABCs greater than FG size 6. Inexpensive intra-esophageal IABCs are technical suitable for the accurate measurement of dynamic Pes during high-frequency respiratory mechanics encountered during infant artificial ventilation.

Air↗

PubMed1997

An evaluation of exercise cardiac output using the CO2 rebreathing extrapolation technique.

We investigated the reproducibility of the carbon dioxide (CO2) rebreathing extrapolation technique of Defares to determine the mixed venous partial pressure of CO2 (PvCO2) using a direct, rather than the commonly used indirect, extrapolation method. The PvCO2 determinations were made five times a day on four subjects who exercised for 4 h daily on a bicycle ergometer over a period of 13 days. The concentration of CO2 in the rebreathing bag was monitored continuously using a rapid-response infrared capnograph. The mean standard deviation was 1.56 mmHg (0.21 kPa) for a mean PvCO2 of 47.6 mmHg (6.3 kPa), giving a mean coefficient of variation of 3.3%. This level of reproducibility agrees favourably with the reliability of direct measurements of pulmonary arterial partial pressure of CO2. We conclude that the CO2 rebreathing extrapolation technique can give reproducible PvCO2 values when a direct method of extrapolation is used.

Adult↗

PubMed1997

Effects of training volume on sleep, psychological, and selected physiological profiles of elite female swimmers.

Excessive training is reported to cause sleep disturbances and mood changes. We examined sleep and psychological changes in female swimmers across a competitive swimming season, that is, at the start of the season (onset), during peak training period (peak), and after a precompetition reduction in training (taper). For each phase, polysomnographic recordings, body composition, psychological parameters, and swimming performance were obtained. A daily training log and sleep diary were maintained for the entire study period. Sleep onset latency (SOL) time awake after sleep onset, total sleep time (TST), and rapid eye movement (REM) sleep times were similar at all three training levels. Slow wave sleep (SWS) formed a very high percentage of total sleep in the onset (26%) and peak (31%) training periods, but was significantly reduced following precompetition taper (16%), supporting the theory that the need for restorative SWS is reduced with reduced physical demand. The number of movements during sleep was significantly higher at the higher training volumes, suggesting some sleep disruption. In contrast to other studies, mood deteriorated with a reduction in training volume and/or impending competition.

Adolescent↗

PubMed1996

Lipoprotein (a) and cholesterol in body builders using anabolic androgenic steroids.

We examined the influence of self-administered anabolic androgenic steroids (AAS) on the lipogram of male body builders. Serum lipoprotein (a) (Lp(a)), total cholesterol, low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C) levels were measured in 10 experimental and 8 control male competitive body builders. The proportion of subjects with serum Lp(a) levels above 30 mg.dl-1 was significantly lower in the AAS group than the non-AAS group. HDL-C levels were significantly lower and LDL-C levels significantly higher in the AAS group than the non-AAS group. These data suggest that AAS in male body builders have a beneficial effect on serum Lp(a) levels but reduce the HDL-C:LDL-C ratio.

Adult↗

PubMed1996

Differences in ultra-endurance exercise in performance-matched male and female runners.

Our study investigated endurance performances in a performance-matched (running 42.2 km) group of females (N = 10) and males (N = 10). The distances examined were 10 km, 21.1 km, 42.2 km, and 90 km. Measurements included VO2max, running economy, lactate accumulation, and running speeds. Although our female subjects performed as well as their male counterparts at 42.2 km (194.8 +/- 12.9 m.min-1 vs 192.6 +/- 16.3 m.min-1), the performance for 90 km was significantly better (P < 0.05) in the female group (171.0 +/- 11.7 m.min-1 vs 155.2 +/- 14.7 m.min-1). The average fraction of the VO2max (F) sustained by each subject indicated that the females achieved their performances by working at a higher (P < 0.01) F (73.4 +/- 5.5% vs 66.3 +/- 3.7% for 42.2 km and 59.8 +/- 6.2% vs 50.2 +/- 3.1% for 90 km). The degree of decline in the fraction of the VO2max sustained as the distance of running increased was significantly less (P < 0.05) in the females. The better performance by the females at 90 km was not related to greater maximal aerobic capacity, running economy, training level, or fatty acid metabolism.

Adult↗

PubMed1994

Prolonged endurance exercise and sleep disruption.

To determine whether exercise duration effects the recovery sleep following exercise, eight fit male endurance athletes, ages 23-42 yr, had their sleep electrophysiologically studied. This was done on four separate occasions: after a day on which no specific exercise was performed; after a day of a 15-km run; after a 42.2-km run day; after a day in which the athletes participated in a strenuous ultra-triathlon. Sleep patterns following the no exercise day and the 15-km and the 42.2-km run days were similar. The sleep pattern of the ultra-triathlon day when compared with the other three days showed significantly increased wakefulness and delayed and decreased rapid eye movement (REM) sleep. The duration of slow wave sleep (SWS) in the first 6 h after lights out, however, was no different. The increased wakefulness and decreased REM clearly indicate increased stress after the ultra-triathlon. REM sleep appears to be a more sensitive index of exercise induced stress than SWS.

Adult↗

PubMed1993

Influence of ketanserin on regional myocardial blood flow after myocardial infarction in baboons.

Serotonin (5-hydroxytryptamine, 5-HT) mediates vasoconstriction and vasodilation in normal coronary circulation of various animal species. In the presence of coronary artery disease, serotonin may inhibit coronary collateral formation and stimulate predominantly vasoconstriction. We tested the effect of ketanserin, a selective 5-HT2 receptor antagonist and platelet aggregation inhibitor, on ischemic myocardium blood flow (BF) and collateral formation after coronary artery occlusion in primates. Fifteen baboons were subjected to left anterior descending coronary artery (LAD) ligation and thrombus formation. Hemodynamics and regional myocardial blood flow (RMBF) (microsphere technique) were measured before and 45 min and 1 week after coronary artery occlusion. There was no significant difference in the hemodynamic measurements, gross infarct size, or infarct-ischemic zone MBF in the experimental group (ketanserin 1 mg/kg daily, n = 9) as compared with the control group (injectable water, n = 6). Both groups had a significant increase in BF ratio of infarct-ischemic/normal myocardium at 1 week as compared with shortly after coronary occlusion. Thus, selective 5-HT2 receptor blockade has neither an adverse nor a protective effect on myocardial infarct resulting from acute thrombotic coronary occlusion in baboons.

Animals↗

PubMed1988

Daily exposure to forty percent oxygen causes a decrease in platelet count.

A study was undertaken to evaluate a previous observation made in this laboratory that hyperoxic treadmill training is associated with a decrease in the circulating platelet count (PLT). The subjects studied breathed air containing 40% oxygen for 30 min/day, 5 days/week, for 6 weeks, while at rest in the seated position. Such exposure resulted in a consistent fall in PLT between day 1 and day 5 of each week (P less than .01). In addition, there was a progressive decline in PLT over the 6 weeks of exposure to the hyperoxic air, PLT being inversely correlated with the duration of hyperoxic exposure (rs = -0.886, P less than .02). The total decrease in PLT over the 6 weeks was 56 +/- 46 x 10(9) l(-1) (P less than .025). Not surprisingly, these changes were mirrored in the plateletcrit (Pct). The decrease in PLT did not appear to be secondary to either hemodilution or reduced erythropoietic stimulation. The mechanism of production and the biological significance of these changes remain to be elucidated.

Administration, Inhalation↗

PubMed1988

Effects of angiotensin converting enzyme inhibition and beta-blockade on exercise responses in hypertensive patients.

We compared exercise responses in two groups of hypertensive patients treated with an angiotensin converting enzyme (ACE) inhibitor (lisinopril, 20-80 mg/day, n = 17) or a cardioselective beta-blocker (atenolol, 50-200 mg/day, n = 9). Measurements were made at rest and during exercise at 25 W (2.7 mets) and at 50 W (3.8 mets) on a bicycle ergometer (where mets is exercising oxygen consumption/resting oxygen consumption) after 4 weeks of placebo, and again after 12 weeks of drug administration. Both drugs reduced (P less than 0.05) mean arterial pressure. Atenolol caused significant decreases in the heart rate (approximately 25%) and cardiac output (approximately 26%; Defares CO2 rebreathing), and significant increases in total peripheral resistance (approximately 30%) and arteriovenous O2 content (approximately 20%). Lisinopril decreased (P less than 0.05) stroke volume. At the same exercise intensity systolic blood pressure, arteriovenous O2 and total peripheral resistance were lower (P less than 0.05) and the heart rate was higher (P less than 0.05) after lisinopril than after atenolol. After the treatment of hypertension with the ACE inhibitor the responses to exercise were less restrictive than those after treatment with the cardioselective beta-blocker.

Atenolol↗

PubMed1988

Submaximal exercise effects on sleep patterns in young women before and after an aerobic training programme.

We studied the sleep patterns of nine young women when sedentary (untrained) and following a 12 week physical fitness training programme. A comparison of baseline sleep patterns and of sleep patterns following one hour of submaximal exercise performed in the evening was carried out at 0 and 12 weeks. The submaximal exercise task was for each subject to cycle for one hour at 70% of her maximal oxygen consumption (VO2 max) as measured when untrained and on completion of the training programme respectively. Changes in fitness were assessed by changes in VO2 max and anaerobic threshold (AT). On the day leading to the all night baseline sleep recordings the subjects carried out their normal daily routines and did no specific exercise. Lean body mass (LBM) was calculated from total body potassium measurements before and after training. A significant improvement in cardiorespiratory fitness did not result in any changes in baseline sleep parameters. The response to the submaximal exercise was an increase in stage 2 NREM sleep and a decrease in slow-wave sleep (SWS, stages 3 & 4) which is possibly indicative of a stress effect. However, in the trained compared to the untrained state, SWS was significantly higher after an exercise load.

Adult↗

PubMed1985

Biochemical responses during recovery from maximal and submaximal swimming exercise.

We set out to demonstrate whether changes in plasma volume, haematocrit and some important blood constituents occurred after swimming 100 m and 800 m, as well as monitoring the duration of these changes. We measured exercise-induced changes in concentration of plasma constituents in eight subjects, and determined the expected effects of haemoconcentration on these constituents. We also investigated the different biochemical responses occurring after maximal exercise (100 m), as compared to submaximal exercise (800 m). The haematocrit increased significantly after the 100 m swim and to a lesser extent after the 800-m swim, returning to basal levels within 30 min. The plasma volume decreased by 16% on completion of the 100 m and by 8% on completion of the 800 m. The blood lactate concentration increased 15-fold and 10-fold after the 100-m and 800-m swims respectively. The plasma potassium concentration increased significantly immediately on completion of the 100-m swim, then decreased significantly at 2 1/2 and 5 min post-exercise, returning to near-basal values at 30 min. The potassium concentration measured after the 800-m event did not differ significantly from basal levels, however the measured concentrations were significantly lower than the concentrations expected on the basis of haemoconcentration. The plasma sodium concentrations measured after both 100-m and 800-m swims were significantly increased. However, calculations correcting for haemoconcentration showed significant losses in total circulating sodium.

Adult↗