Biomedical subjects

Michael A Welsch

Publications and source records attributed to Michael A Welsch.

8 recordsLinked to original sources

PubMed2007

Regional changes in reactive hyperemic blood flow during exercise training: time-course adaptations.

BACKGROUND: Few studies have examined the time-course of localized exercise training on regional blood flow in humans. The study examined the influence of handgrip exercise training on forearm reactive hyperemic blood flow and vascular resistance in apparently healthy men. METHODS: Forearm blood flow and vascular resistance were evaluated, in 17 individuals [Age: 22.6 +/- 3.5], in both arms, at rest and following 5 minutes of arterial occlusion, using strain gauge plethysmography, prior to training (V1) and every week thereafter (V2-5) for 4 weeks. Handgrip exercise was performed in the non-dominant arm 5 d/wk for 20 minutes at 60% of maximum voluntary contraction, while the dominant arm served as control. RESULTS: Resting HR, BP, and forearm blood flow and vascular resistance were not altered with training. The trained arm handgrip strength and circumference increased by 14.5% (p = 0.014) and 1.56% (p = 0.03), respectively. ANOVA tests revealed an arms by visit interaction for the trained arm for reactive hyperemic blood flow (p = 0.02) and vascular resistance (p = 0.009). Post-hoc comparison demonstrated increased reactive hyperemic blood flow (p = 0.0013), and decreased post-occlusion vascular resistance (p = 0.05), following the 1st week of training, with no significant changes in subsequent visits. CONCLUSION: The results indicate unilateral improvements in forearm reactive hyperemic blood flow and vascular resistance following 1 week of handgrip exercise training and leveled off for the rest of the study.

Journal Article↗

PubMed2006

Biphasic responses of the brachial artery diameter following forearm occlusion: a blunted response in the elderly.

BACKGROUND: The purpose was to examine the temporal response of the brachial artery diameter following 5 minutes of forearm occlusion in young men. A secondary objective was to compare the main features of the temporal pattern between young and old. METHODS: Sixteen young (28 +/- 8 yrs) and fifteen older (85 +/- 8 yrs) men underwent high-resolution ultrasonography of the brachial artery before and after five minutes of forearm occlusion. RESULTS: Following release of the pressure cuff the brachial artery diameter exhibits a temporal biphasic response. Initially, there is a significant reduction in brachial diameter (NIL) compared to baseline (BASE), followed by a rapid increase to a PEAK at 41 sec post release. When comparing the magnitude of the decrease in diameter and the Brachial Artery Flow Mediated Dilation (BAFMD) between Young and Old, older subjects demonstrated a blunted response (Magnitude of Decrease: Young: 2.0%; Old: 0.4%, p = 0.015, and BAFMD: Young: 7.7%; Old: 2.3%, p = 0.001). Finally, a significant relationship was noted between the magnitude of decrease and BAFMD (r = -0.44, p = 0.04). CONCLUSION: Examination of the temporal response of the brachial artery diameter following 5 minutes of forearm occlusion reveals a biphasic pattern in all participants. Specific features of this pattern are blunted in older adults compared with younger subjects. Finally, the magnitude of the drop in diameter following forearm occlusion correlates with the magnitude of the BAFMD.

Journal Article↗

PubMed2003

Measurements of vascular function using strain-gauge plethysmography: technical considerations, standardization, and physiological findings.

The main purpose of the present study was to examine the relationships between measures of fitness [estimated peak oxygen consumption (V(O2) peak) and handgrip strength] and forearm vascular function in 55 young (22.6 +/- 3.5 yr) adults. In addition, the present study considered methodological and technical aspects regarding the examination of the venous system using mercury in-Silastic strain-gauge plethysmography (MSGP). Forearm venous capacitance and outflow were examined using five different [7, 14, 21, 28, and 35 mmHg < diastolic blood pressure (DBP)] venous occlusion pressures and after a 5- and 10-min period of venous occlusion. A pressure of 7 mmHg < DBP and a period of 10 min venous occlusion produced the greatest (P < 0.05) venous capacitance and outflow, without altering arterial indexes. Reproducibility of forearm arterial and venous indexes were evaluated at rest and after 5 min of upper arm arterial occlusion at 240 mmHg on three different occasions within 10 days with the interclass correlation coefficient ranging from 0.70 and 0.94. Estimated V(O2) peak correlated with postocclusion arterial inflow (r = 0.54, P = 0.012) and resting venous outflow (r = 0.56, P = 0.016). Finally, handgrip strength was associated with venous capacitance (r = 0.57, P = 0.007) and outflow (r = 0.67, P = 0.001). These results indicate that the examination of forearm vascular function using MSGP is reproducible. Moreover, the data show the importance of careful consideration of the selection of venous occlusion pressure and period when implementing these measures in longitudinal trials. Finally, the associations between fitness and venous measures suggest a link between venous function and exercise performance.

Adult↗

PubMed2003

Time course of improved flow-mediated dilation after short-term exercise training.

PURPOSE: The purpose was to determine the influence of a unilateral localized short-term handgrip training protocol on brachial artery flow-mediated dilation (BAFMD) and to examine the time course of such changes. METHODS: Fourteen healthy males (age: 26 +/- 5.7 yr) underwent high-resolution ultrasonographic brachial artery assessments before (V1), during (V2-V7), and at the end of 4 wk (V8) of 60% maximal voluntary contraction handgrip training (20 min.d-1, 5 d.wk-1) of the nondominant arm. RESULTS: Before training resting diameters were similar between the trained (nondominant) and untrained (dominant) arms. A 2 (trained and untrained arms) x 2 (V1 and V8) repeated measure ANOVA revealed a significant main (P = 0.02 and P = 0.03) and interaction effect (P = 0.05 and P = 0.01) for the percent and absolute change in BAFMD. BAFMD improved 62% and 70%, respectively from V1 to V8, for the percent and absolute change. Subsequent linear orthogonal polynomial contrasts indicate both the percent and absolute change in BAFMD were statistically different at V2 (end of week 1 and 4 training days) from V1. These unilateral changes were not accompanied by changes in resting artery diameter, hemodynamic measures, hematological markers, and indices of heart rate variability suggesting the change may be locally mediated. CONCLUSIONS: This study shows a localized short-term exercise-training program resulted in significant improvements in BAFMD in the trained arm compared with the untrained arm and suggests this occurred after only 4 d of training.

Adaptation, Physiological↗

PubMed2003

Influence of short-term endurance exercise training on heart rate variability.

PURPOSE: To examine the influence of 2 wk (eight sessions) of endurance training on cardiac autonomic modulation, as measured by heart rate variability (HRV). METHODS: Twenty-four males (mean age: 23.1 yr) were randomized to an exercise (EX; N = 12) or control group (CT; N = 12). EX trained for eight sessions (4x wk-1, 40 min, 80-85% HRreserve) on a cycle ergometer. ECG tracings were collected during 5 min of paced breathing (12 breaths x min-1 (PB)), 5 min of spontaneous breathing (SB1), 5 min of 70 degrees head-up tilt (TILT), and a second 5-min period of spontaneous breathing (SB2). Data were collected before (test 1), during (tests 2-4), and 48 h after (test 5) the 2-wk period. HRV was reported as the standard deviation of RR intervals, and as natural logarithm of the normalized units (NU) of high- and low-frequency power (lnHF and lnLF). RESULTS: EX exhibited a significant increase in peak oxygen consumption (8%). During PB and TILT conditions, ANOVA revealed a group x time interaction such that EX exhibited lower lnLFNU and lnLF/lnHF during test 5 compared with test 1. CONCLUSION: These data suggest that eight endurance exercise-training sessions performed over 2 wk enhance the relative vagal modulation of the heart during PB and TILT, but not during SB.

Adult↗

PubMed2002

Substrate utilization during exercise in postmenopausal women on hormone replacement therapy.

It has been suggested that due to the slight direct or indirect effect of estrogen on lipolytic activity, the age-related decrease in production associated with the menopause may heighten the risk of cardiovascular and metabolic disease in women. While hormone replacement therapy (HRT) alone may have little or no effect on body mass in postmenopausal women, data suggest it can alter the shift toward abdominal adiposity. Furthermore, estrogen may have a synergistic effect on exercise-induced reduction in fat mass. Accordingly, the purpose of this investigation was to examine the potential influence of HRT on substrate utilization during 30 min of treadmill exercise at approximately 80% maximal oxygen uptake (VO(2max)) in postmenopausal women. Eight women were receiving HRT and nine women were not (NHRT). No significant differences between the HRT and NHRT groups were noted for age, body mass, body fat, VO(2max) or the percentage of VO(2max) maintained during exercise. Expired gas samples were analyzed every 30 s to determine respiratory exchange ratio (R) and % VO(2max). The R, total energy expended and percentage contributions from fats and carbohydrate were averaged over three periods during the exercise (min 1-10, 11-20, and 21-30). There was no effect of HRT on R, total energy expended or substrate contribution. Thus, treatment of postmenopausal women using HRT (primarily conjugated equine estrogens in doses of 0.625-1.25 mg x day(-1)) did not appear to affect the percentages of fat and carbohydrate utilized during 30 min of treadmill exercise at 80% of VO(2max). However, the exercise responses in this group of menopausal women were consistent with a duration-dependent increased reliance on fat as an energy source during exercise of moderate to vigorous intensity as has been demonstrated in younger populations.

Aged↗

PubMed2002

Stability and reproducibility of brachial artery flow-mediated dilation.

PURPOSE: Brachial artery flow-mediated dilation (BAFMD) is a noninvasive technique, which has been suggested as a potential means of identifying patients with early atherosclerosis and therefore has enormous clinical appeal. Despite this, the stability and reproducibility of this technique are not yet clear. Therefore, the purpose of this study was to establish the stability and reproducibility of BAFMD after 5 min of forearm occlusion and to produce power calculations to aid in clinical trial design. METHODS: Twenty-six healthy volunteers underwent high-resolution ultrasonographic brachial artery assessments before, during, and after 5 min of forearm occlusion. The study design involved three scans on 2 d, performed by two ultrasonographers and analyzed by two readers. All subjects were tested between 7 and 11 a.m. after refraining from food and exercise. The nondominant arms were scanned, in longitudinal view, approximately 4 cm proximal to the olecranon process, in the anterior/medial plane. Blood draws were performed on each visit. The SAS MIXED restricted maximum likelihood (REML) procedure for an unbalanced design was used to calculate variance components and provide power calculations. RESULTS: Average baseline artery diameter for all studies was 3.48 +/- 0.53 mm. This increased to 3.71 +/- 0.57 mm (6.58 +/- 4.15%) at peak dilation. Intraclass correlation coefficients (ICCC) for days, testers, and readers were 0.92, 0.94, and 0.90, respectively. To detect a difference in vasoreactivity of 60% (two-tailed), e.g., 5% vasodilation versus 8% vasodilation, at 90% power, 23 and 10 subjects would be required for cross-sectional and pre-post designs, respectively. CONCLUSIONS: These data indicate adequate stability and reproducibility of the BAFMD technique under controlled conditions. Additionally, BAFMD appears useful to differentiate between groups, although its prognostic value for the examination of individuals is unclear.

Adult↗

PubMedDate not supplied

Influence of venous function on exercise tolerance in chronic heart failure.

PURPOSE: The clinical phase of chronic heart failure (HF) includes a marked decline in exercise tolerance, in part due to impaired skeletal muscle blood flow delivery. Interestingly, the role of the venous system on exercise tolerance in patients with HF has not received much attention, despite evidence of changes in venous structure and function. The purpose of this study was to examine the relationship between forearm arterial and venous function, and exercise tolerance in patients with HF and age-matched controls. METHODS: Vascular function and exercise tolerance was examined in 20 patients with HF (age 59 +/- 13 years) and 10 control subjects (age 51 +/- 16 years). Nondominant forearm arterial inflow, vascular resistance, venous capacitance, and venous outflow were evaluated at rest and after 5 minutes of upper arm occlusion, using strain gauge plethysmography. Exercise tolerance was measured as the maximum walking distance achieved on a 6-minute walking test. RESULTS: Maximum walking distance (HF: 178 +/- 65 m; controls: 562 +/- 136 m, P=.0001), and forearm vascular function after occlusion were significantly different between groups (forearm arterial inflow: HF 15.3 +/- 6; controls 22 +/- 6.7; forearm venous capacitance: HF 1.4 +/- 0.5; controls 2.0 +/- 0.4; forearm venous outflow: HF 24.5 +/- 9.4; controls: 33 +/- 10 mL x 100 mL tissue(-1) x min(-1); and forearm vascular resistance: HF 7.8 +/- 3; controls 4.6 +/- 1.4 U). Correlation analysis revealed significant associations between all forearm vascular measurements after occlusion and maximum walking distance. CONCLUSION: These data confirm previous studies indicating the importance of arterial reactivity on exercise tolerance in patients with HF. Additionally, the results suggest the importance of venous function as a contributing factor to exercise performance.

Adult↗