Citations

We tested the hypothesis that administering low‐dose dopamine (2 mcg/kg/min) to desensitize the carotid body chemoreceptors would alter metrics of heart rate variability (HRV). Electrocardiogram (ECG) recordings were obtained from 18 healthy adults (age = 31 ± 2 years; BMI = 24.6 ± 0.6 kg/m 2 ) during two randomized study days where they received an IV infusion of saline (S) or dopamine (DA). HRV was analyzed during five minute segments at baseline and during infusions of S and DA. Time‐domain analysis of the root mean square of the successive differences (RMSSD) along with spectral domain analysis of low (LF) and high frequency (HF) were obtained. There were no differences (P > 0.05) in respiration rate or blood pressure at any time point. Heart rate increased from baseline during DA (60 ± 2 vs. 63 ± 2 bpm; P < 0.01) and during infusion it was greater in DA vs. S (63 ± 2 vs. 58 ± 2 bpm; P < 0.01). RMSSD decreased from baseline to infusion during DA (68.2 ± 7.6 vs. 51.6 ± 6.0 ms; P < 0.01) and during infusion it was lower in DA vs. S (78.3 ± 10.3 vs. 51.6 ± 6.0 ms; P < 0.01). HF was reduced during DA vs. baseline (1733± 301 vs. 870 ± 171 ms 2 ; P < 0.01), and during infusion DA was also lower than S (1936 ± 471 vs. 870 ± 171 ms 2 ; P = 0.02). There were no changes (P > 0.05) in LF, LF/HF or normalized HF and LF values. These data indicate that during resting conditions the carotid body chemoreceptors likely modulate parasympathetic components of HRV in healthy adults. Grant Funding Source : Supported by NIH R01DK090541 and RO1HL61388

Background The baroreflex plays an integral role in blood pressure maintenance by altering heart rate and sympathetic activity in response to changes in arterial pressure. Baroreflex sensitivity (BRS) has been shown to decrease linearly during progressive exposure to central hypovolemia as induced by lower body negative pressure (LBNP), and can be used as an index of decompensation status during hemorrhage. Circulating epinephrine is significantly elevated during high stress situations such as hemorrhage; however, it is unclear whether epinephrine influences BRS during progressive exposure to central hypovolemia. Based on previous work, we hypothesized epinephrine would attenuate any reduction in spontaneous cardiac baroreflex sensitivity during LBNP. Methods Ten young (35±3 yrs), healthy (BMI 24±1 kg/m 2 ) men and women (6M/4F) underwent LBNP protocols on 2 separate days consisting of a 10‐min pre‐infusion baseline, 15‐min infusion period (randomized to saline or epinephrine, 0.1 μg/kg/min), 10‐min post‐infusion baseline, and 5 minutes of LBNP at −15, −30, −45, −60, −70, and −80 mmHg until the onset of presyncope (range= −30 to −80 mmHg). Presyncope was defined as a rapid decrease in systolic blood pressure greater than 15 mmHg, systolic blood pressure less than 80 mmHg, bradycardia, or voluntary termination due to presyncopal symptoms. Heart rate (HR; electrocardiogram) and blood pressure (BP; radial arterial catheter) were recorded continuously. Spontaneous cardiac BRS was determined using the sequence method (WinCPRS). Data are reported from both 10‐min baselines and from 1 minute at 20, 40, 60, 80, and 100 percent of each individual's total LBNP exposure time. Results We observed no significant differences in total exposure time (1475±150 vs. 1415±79s; p=0.69) or cumulative stress index (820±135 vs. 699±69 min*mmHg; p=0.37) between saline and epinephrine visits, respectively. Baroreflex sensitivity did not change during post‐infusion baselines (ΔDown‐Down =−2±1 vs. −2±2 ms/mmHg; saline vs. epinephrine, respectively; p=0.09). Baroreflex sensitivity was significantly reduced with LBNP (p<0.01 main effect of LBNP). There was no difference between the change in baroreflex sensitivity during LBNP with saline or epinephrine infusion (ΔDown‐Down =−14±4 vs. −8±4 ms/mmHg, p=0.17). Conclusions Consistent with previous work, spontaneous cardiac baroreflex sensitivity fell during LBNP. Contrary to our hypothesis, epinephrine infusion did not attenuate the fall in spontaneous cardiac baroreflex sensitivity observed during simulated blood loss. Because epinephrine did not alter the effect of LBNP on BRS, these data suggest that BRS may accurately reflect decompensation status during traumatic hemorrhage independent of elevated circulating epinephrine. Support or Funding Information US Army Medical Research and Materiel Command Contract W81XWH‐13‐2‐0038

Due to the relationship between stroke volume (SV) and pulse pressure (PP) during lower body negative pressure (LBNP), we hypothesized that PP reflects SV during hemorrhage (HEM). After a 5‐minute baseline, 6 men were exposed to LBNP at ‐15, ‐30, and ‐45 mmHg for 5 minutes at each pressure. After 45 minutes of recovery, three progressive 333‐ml stages of HEM (1 L total) were performed. SV was assessed using a CC Nexfin and PP was calculated using an arterial catheter. SV (111 ± 2.1 vs. 77 ± 6.7 mL; p = 0.04) and PP (58±2.7 vs. 41 ± 4.3 mm Hg; p = 0.03) decreased from baseline to ‐45 mmHg LBNP. SV (118 ± 4.4 to 99 ± 6.8 mL; p = 0.06) and PP decreased (58 ± 2.9 to 48 ± 4.9 mmHg; p = 0.06) from baseline to ‐1 L of HEM. PP correlated with SV during HEM (amalgamated r 2 = 0.98) and LBNP (amalgamated r 2 = 0.99). There was limited inter‐subject variability in PP vs. SV during LBNP ( r 2 range 0.57 to 0.99, 5/6 had an r 2 >; 0.90), but substantial inter‐subject variability during HEM ( r 2 range 0.21 to 0.99, 2/6 had an r 2 >; 0.90). Reductions in PP induced by LBNP or HEM are strongly correlated with SV. However large inter‐individual differences in this correlation during HEM, which may indicate a significantly variable compensatory response in human arterial distensibility, may limit the use of PP as a surrogate for SV during clinical blood loss. Funded by U.S. Army MRMC Combat Casualty Care Research Program Grant # W81XWH‐11–1‐0823.

Background Lower body negative pressure (LBNP) increases carotid body chemosensitivity. Whether the increase in chemosensitivity is functionally significant in the hemodynamic response to LBNP was previously unknown. We tested the hypothesis that desensitization of the carotid body chemoreceptors would improve the hemodynamic response to LBNP. Methods Ten healthy, non‐obese male subjects (35 ± 3 years, BMI: 25 ± 1 kg/m 2 ) completed 2 study visits (Saline, Dopamine), separated by a minimum of 4 weeks. Intravenous dopamine was infused at an individualized dose (1–2 mg/kg/min) shown to maximally blunt the hypoxic ventilatory response (a measure of carotid body chemosensitivity). Arterial blood pressure (brachial catheter) and heart rate (ECG) were continuously recorded. On each study day subjects underwent step‐wise exposures of LBNP (−15, −30, and −45 mmHg) to simulate hemorrhage. Cumulative stress index (CSI) was calculated by summating the product of negative pressure (mmHg) by the time (min) during each LBNP level (−15, −30, and −45 mmHg). Results Dopamine tended to reduce CSI (Saline: 503 ± 52; Dopamine: 408 ± 45 mmHg*min; p=0.07). Changes in heart rate from baseline during graded LBNP were not statistically distinguishable between Saline and Dopamine conditions (− 15 mmHg: +4 ± 1 vs +3 ± 2 BPM, p=0.99; − 30 mmHg: +12 ± 1 vs +12 ± 3 BPM, p=0.99; − 45 mmHg: HR +21 ± 2 vs +19 ± 5 BPM, p=0.99). Similarly, change in systolic blood pressure from baseline during graded LBNP was not different between Saline and Dopamine conditions (− 15 mmHg: +1 ± 1 vs −1 ± 2 mmHg p=0.99; − 30 mmHg: −7 ± 3 vs −6 ± 4 mmHg, p=0.99; − 45 mmHg: −12 ± 4 vs −22 ± 6 mmHg, p=0.19). However, change in diastolic blood pressure from baseline during graded LBNP was higher at −45 mmHg between Saline and Dopamine conditions (− 15 mmHg: +2 ± 1 vs −0 ± 1 mmHg p=0.47; − 30 mmHg: −1 ± 2 vs −2 ± 2 mmHg p=0.26; − 45 mmHg: −2 ± 2 vs −12 ±3 mmHg, p=0.0004). Conclusions Desensitization of the carotid body chemoreceptors reduced diastolic blood pressure responses to LBNP at −45 mmHg only, with minimal effect at lower levels. These data suggest chemoreflex activity during LBNP may be functionally significant in the blood pressure responses only during higher levels of simulated hemorrhage. Support or Funding Information Funding: W81XWH‐13‐2‐0038 (DOD)

Hypovolemia‐induced sympathoexcitation might initiate an immune response through an increase in circulating epinephrine and splenic demargination. We tested the hypothesis that lower body negative pressure (LBNP) and blood loss (BL) result in comparable increases in white blood cell counts (WBCs). We determined WBCs and epinephrine levels in 12 men who performed a LBNP and BL protocol in a randomized order. LBNP consisted of 5‐minute stages at 0, ‐15, ‐30, and ‐45 mmHg of suction. BL included 5 minutes at baseline and following three stages of 333 mL of blood removal (up to 1000 mL total). Blood draws were performed at baseline and after the last stage of each protocol. LBNP to −45mmHg was a greater central hypovolemic stimulus vs. BL, therefore WBCs and epinephrine concentrations were plotted against central venous pressure (CVP) to obtain stimulus‐response relationships using the linear regression line slopes for both protocols. Paired tests were used to determine if the slopes of these regression lines fell on similar trajectories for each protocol. Mean regression line slopes fell on similar trajectories for total WBC (LBNP 183±46 vs. BL 155±109 mcL −1 *mmHg −1 , p=0.15), neutrophils (LBNP 110±29 vs. BL 96±72 mcL −1 *mmHg −1 , p=0.15) and lymphocytes (LBNP 65±21 vs. BL 59±38 mcL −1 *mmHg −1 , p=0.90). Mean regression line slopes for epinephrine were similar as well (LBNP 15±5 vs. BL 16±4 pg *mL −1 *mmHg −1 , p=0.84). Our results indicate that LBNP models the stimulus‐response relationship between CVP and WBCs observed during BL. Central hypovolemia, induced by LBNP or BL, elicits a relative leukocytosis with a predominantly neutrophil‐based response. Support or Funding Information US Army MRMC Combat Casualty Care Research Program Grant # W81XWH‐11‐1‐0823

Background: The US Food and Drug Administration authorized COVID-19 convalescent plasma (CCP) therapy for hospitalized COVID-19 patients via the Expanded Access Program (EAP) and the Emergency Use Authorization (EUA), leading to use in about 500,000 patients during the first year of the pandemic for the USA. Methods: We tracked the number of CCP units dispensed to hospitals by blood banking organizations and correlated that usage with hospital admission and mortality data. Results: CCP usage per admission peaked in Fall 2020, with more than 40% of inpatients estimated to have received CCP between late September and early November 2020. However, after randomized controlled trials failed to show a reduction in mortality, CCP usage per admission declined steadily to a nadir of less than 10% in March 2021. We found a strong inverse correlation (r = −0.52, p=0.002) between CCP usage per hospital admission and deaths occurring 2 weeks after admission, and this finding was robust to examination of deaths taking place 1, 2, or 3 weeks after admission. Changes in the number of hospital admissions, SARS-CoV-2 variants, and age of patients could not explain these findings. The retreat from CCP usage might have resulted in as many as 29,000 excess deaths from mid-November 2020 to February 2021. Conclusions: A strong inverse correlation between CCP use and mortality per admission in the USA provides population-level evidence consistent with the notion that CCP reduces mortality in COVID-19 and suggests that the recent decline in usage could have resulted in excess deaths. Funding: There was no specific funding for this study. AC was supported in part by RO1 HL059842 and R01 AI1520789; MJJ was supported in part by 5R35HL139854. This project has been funded in whole or in part with Federal funds from the Department of Health and Human Services; Office of the Assistant Secretary for Preparedness and Response; Biomedical Advanced Research and Development Authority under Contract No. 75A50120C00096.

AbstractIn the absence of effective countermeasures, human convalescent plasma has been widely used to treat severe acute respiratory syndrome coronavirus 2, the causative agent of novel coronavirus disease 19 (COVID‐19), including among patients with innate or acquired immunosuppression. However, the association between COVID‐19‐associated mortality in patients with immunosuppression and therapeutic use of convalescent plasma is unknown. We review 75 reports, including one large matched‐control registry study of 143 COVID‐19 patients with hematological malignancies, and 51 case reports and 23 case series representing 238 COVID‐19 patients with immunosuppression. We review clinical features and treatment protocols of COVID‐19 patients with immunosuppression after treatment with human convalescent plasma. We also discuss the time course and clinical features of recovery. The available data from case reports and case series provide evidence suggesting a mortality benefit and rapid clinical improvement in patients with several forms of immunosuppression following COVID‐19 convalescent plasma transfusion. The utility of convalescent plasma or other forms of antibody therapy in immune‐deficient and immune‐suppressed patients with COVID‐19 warrants further investigation.

World-class athletes are substantively faster, wearing marathon racing shoes with technological advancements than other shoes when competing in the marathon. Our findings suggest that technological advances in footwear contributed to the recent improvements in marathon finishing times among elite runners and in record-setting marathon performances. This investigation highlights the importance of sports analytics and may have broad implications for the regulation of running footwear during competition.

Abstract Elite performing men continue to record faster record times in running events compared to women. These sex‐based differences in running speed and endurance in humans are expected based on sexual dimorphisms that contribute to differences in the determinants of aerobic performance. Comparatively, the sexual dimorphisms contributing to sex‐based differences in elite aerobic performance are not ubiquitous across other species that compete in running events. The purpose of this review is to offer a framework and model for ongoing discussions of the physiological determinants and ultimately limits of physical performance. The records for average running speed of champion athletes were delineated by sex for thoroughbred horses, greyhound dogs, and humans. Male and female performances within each of these species are being optimized by training, nutrition, and financial incentives, and are approaching a performance maximum. For horses and greyhounds breeding also plays a role. Analysis of athletic records shows that there is a sex‐related difference of ~10% or more in elite athletic performance for humans; however, the upper limit of performance does not appear to be different between sexes for thoroughbred horses and greyhound dogs. In the context of the nil sex differences in running performance in thoroughbreds and greyhounds, we discuss the physiological role of sexual dimorphisms on sex‐specific limits to running performance. We highlight that studies on both human and animal performance in athletic events stimulate critical physiological questions and drive novel research.