Miller, Andrew D.

Background Central hypovolemia elicited by hemorrhage triggers sympathetically‐mediated baroreflex responses to maintain organ perfusion through peripheral vasoconstriction; humans with low tolerance (LT) to central hypovolemia have a diminished vasoconstrictor response during progressive reductions in central volume. Using the lower body negative pressure (LBNP) hemorrhage model, we tested the hypothesis that humans with LT to central hypovolemia would display attenuated resting beat‐to‐beat neuro‐hemodynamic transduction of muscle sympathetic nerve activity (MSNA) compared to those with high tolerance (HT). Methods MSNA (microneurography, peroneal nerve) and diastolic arterial pressure (DAP; finger photoplethysmography) were recorded in 33 human subjects (23 men, 10 women, age: 31 ± 9 years, BMI: 26 ± 4 kg/m 2 ) who subsequently underwent LBNP to tolerance (onset of pre‐syncopal symptoms) – Figure 1. Consistent with previous studies, subjects were classified as LT if they experienced pre‐syncopal symptoms prior to completing LBNP of −60 mm Hg, or as HT if they experienced pre‐syncopal symptoms after completing LBNP of −60 mm Hg. We performed linear regression analysis on data of binned MSNA burst areas against DAP; the slope of this regression represents transduction. Results Of the 33 subjects, 8 exhibited LT (time to pre‐syncope for LT: 17 ± 2 min and HT: 27 ± 5 min) Contrary to our hypothesis, resting beat‐to‐beat neuro‐hemodynamic transduction was not different between LT and HT subjects (median 0.09 IQR 0.03 – 0.16 mmHg (%s) − 1 vs. median 0.12 IQR 0.06 – 0.16 mmHg (%s) − 1 , respectively, p = 0.44) and was not related to time to pre‐syncope ( p = 0.70). Conclusion Tolerance to simulated blood loss is not related to resting sympathetic neuro‐hemodynamic transduction. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

Pulse Decomposition Analysis (PDA) offers new insights into factors altering the arterial pressure pulse contour. PDA premise is that peripheral arterial pressure pulse envelope consists of distinct component pressure pulses, a left ventricular ejection and its reflections. Two PDA parameters appear to be particularly useful in quantifying the pulse contour. P2P1 is the ratio of second component pulse and primary ejection pulse amplitudes. T13 is the temporal delay between the third component pulse and the primary ejection pulse. P2P1 and T13 parameters were used to examine pressure pulse contour changes in 81 healthy subjects (18–27 yrs; BMI 27.5 ± 2.6) undergoing a Stroop mental stress test, cycle ergometer stress tests (3 min; 50W and 100W), and post‐exercise recovery. Digital pressure pulse contours were recorded/quantified using PDA formalism. Relative to baseline, P2P1 increased 8% post‐Stroop (individual variation 0% to 15%), T13 increased 4%, (individual variation 0% to 8%). Exercise decreased P2P1 21 ± 14%, while the T13 change was 19 ± 15%. PDA‐based pulse propagation model quantifies physical changes that arterial pulse reflection sites undergo. Peripheral arterial pressure pulse appears to be due to the primary ejection pulse and two major reflections. Two reflection sites in the central arteries appear to be responsible for the “reflected” wave part of the pulse contour.

Objective Exercise is a cornerstone of therapeutic intervention for individuals with cystic fibrosis (CF). However, daily breathing treatments (e.g. chest physiotherapy and inhalation of nebulized albuterol) typically last ~90 minutes, providing a time‐barrier to completing daily exercise. Thus, the purpose of our study was to determine the effects of a combination therapy (exercise and nebulized albuterol) on airway function and bronchodilator delivery. We tested the hypotheses that combination therapy (exercise + nebulized albuterol) would 1) augment the bronchodilator effect compared to either intervention alone, and 2) increase the plasma concentration of albuterol compared to nebulized albuterol alone. Methods Participants with CF (n=9, 5 female, 25±2yrs, forced expiratory volume in 1 second (FEV 1 ) =82±5%predicted) first completed a screening visit (V̇O 2max test, cycle ergometer) and then three study visits in a randomized order. During each study visit, participants completed measures of airway function [FEV 1 and forced expiratory flow from 25–75% of forced vital capacity (FEF 25–75 )], and a blood draw (n=8) to determine plasma albuterol concentration. Participants then completed one of three interventions [albuterol only, (A): 2.5mg nebulized albuterol over 15min; exercise only (E): 30min cycling exercise at 50% of peak watts; albuterol and exercise (A+E): 30min cycling exercise at 50% of peak watts with 2.5mg nebulized albuterol nebulized over the last 15min of cycling). Airway function and plasma albuterol were measured at 0, 15, 30, 45, 60, 90, 120, 180, and 240min after the intervention. Additional plasma albuterol measures were taken 5, and 6hrs post intervention. Data are mean±SD. Results Delivery of nebulized albuterol during exercise did not augment or prolong the bronchodilator effect compared to exercise or albuterol alone. The transient improvement in airway function during the interventions—increase in FEV 1 (time=0.050, intervention p=0.166, interaction p=0.135) or increase in FEF 25–75 (time p=0.001, intervention p=0.207, interaction p=0.990) — was not different between the three interventions. Delivery of nebulized albuterol during exercise did not increase the plasma concentration of albuterol compared to nebulized albuterol alone. The maximum plasma concentration of albuterol (C max ) and the area under the curve (AUC) of albuterol concentration over time were not different between interventions (C max = 2.57±1.60 vs. 2.56±1.13ng·mL −1 , p=0.982; AUC 0–6hrs = 6.1±3.6 vs. 6.9±3.3hr·ng·mL −1 , p=0.188; A vs. A+E interventions, respectively). Conclusions Delivery of nebulized albuterol during moderate intensity exercise did not significantly alter bronchodilator effects or plasma levels of albuterol compared to albuterol or exercise alone. These data suggest that delivery of nebulized albuterol during exercise is safe and effective, but does not augment bronchodilator effects or drug delivery. This combination intervention (A+E) may be a time efficient method for individuals with cystic fibrosis to gain therapeutic effects of exercise and breathing treatments. Support or Funding Information F32 HL131151, Cystic Fibrosis Research Inc.

Aging is associated with deterioration in the structure and function of the pulmonary circulation. We characterized the lung diffusing capacity for carbon monoxide (DLCO), alveolar-capillary membrane conductance (DmCO), and pulmonary-capillary blood volume (Vc) response to discontinuous incremental exercise at 25, 50, 75, and 90% of peak work (Wpeak) in four groups: 1) Young [27 ± 3 yr, maximal oxygen consumption (V̇o2max): 110 ± 18% age predicted]; 2) Young Highly Fit (27 ± 3 yr, V̇o2max: 147 ± 8% age predicted); 3) Old (69 ± 5 yr, V̇o2max: 116 ± 13% age predicted); and 4) Old Highly Fit (65 ± 5 yr, V̇o2max: 162 ± 18% age predicted). At rest and at 90% Wpeak, DLCO, DmCO, and Vc were decreased with age. At 90% Wpeak, DLCO, DmCO, and Vc were greater in Old Highly Fit vs. Old adults. The slope of the DLCO-cardiac output (Q̇) relationship from rest to end exercise at 90% Wpeak was not different between Young, Young Highly Fit, Old, and Old Highly Fit (1.35 vs. 1.44 vs. 1.10 vs. 1.35 mlCO·mmHg−1·liter blood−1, P = 0.388), with no evidence of a plateau in this relationship during exercise; this was also true for DmCO-Q̇ and Vc-Q̇. V̇o2max was positively correlated with 1) DLCO, DmCO, and Vc at rest; and 2) the rest to end exercise change in DLCO, DmCO, and Vc. In conclusion, these data suggest that despite the age-associated deterioration in the structure and function of the pulmonary circulation, expansion of the pulmonary capillary network does not become limited during exercise in healthy individuals regardless of age or cardiorespiratory fitness level. NEW & NOTEWORTHY Healthy aging is a crucial area of research. This article details how differences in age and cardiorespiratory fitness level affect lung diffusing capacity, particularly during high-intensity exercise. We conclude that highly fit older adults do not experience a limit in lung diffusing capacity during high-intensity exercise. Interestingly, however, we found that highly fit older individuals demonstrate greater values of lung diffusing capacity during high-intensity exercise than their less fit age-matched counterparts.