Coagulation Changes during Central Hypovolemia across Seasons

Age-dependent seasonality in the incidence of stroke: A 21-year population-based study

INTRODUCTION

Seasonality in the incidence of stroke has been examined in numerous studies, yet data on whether it differs with age are limited. To fill this gap, we utilized a largescale dataset from Israel.

PATIENTS AND METHODS

We retrieved data of all hospitalizations for ischemic stroke (IS), transient ischemic attack (TIA) and intra cerebral hemorrhage (ICH) from 2000 to 2020. We maintained separate datasets for IS/TIA and ICH, divided into five age groups: 18-49, 50-59, 60-69, 70-79, and 80+. We modeled the monthly incidence using a generalized additive model. The seasonal effect was defined by the rate ratio (RR) of each month compared to the annual mean.

RESULTS

The analysis included 317,586 and 23,789 events of IS/TIA and ICH respectively. We found an interaction between age and seasonality, accounting for a phase shift with age in the seasonal pattern of IS/TIA incidence. For cases under 70 years, the peak was during summertime and the RRs increased with decreasing age, reaching 1.11 (95% CI 1.09-1.13) at the youngest age group. In contrast, among the elderly, a winter peak was observed and the RRs increased with age to 1.07 (95% CI 1.06-1.08) at the oldest age group. For ICH, a winter/autumn peak was identified and the RRs increased with age to 1.20 (95% CI 1.16-1.24).

CONCLUSIONS

Our finding of age-dependent seasonal patterns in the occurrence of stroke, suggests closer monitoring of cardiovascular risk factors during wintertime among elderly individuals. The mechanism governing the seasonal phase shift with age in IS/TIA incidence, requires further investigation.

Effects of menstrual cycle on hemodynamic and autonomic responses to central hypovolemia

Background

Estrogen and progesterone levels undergo changes throughout the menstrual cycle. Existing literature regarding the effect of menstrual phases on cardiovascular and autonomic regulation during central hypovolemia is contradictory.

Aims and study

This study aims to explore the influence of menstrual phases on cardiovascular and autonomic responses in both resting and during the central hypovolemia induced by lower body negative pressure (LBNP). This is a companion paper, in which data across the menstrual phases from healthy young females, whose results are reported in Shankwar et al. (2023), were further analysed.

Methods

The study protocol consisted of three phases: (1) 30 min of supine rest; (2) 16 min of four LBNP levels; and (3) 5 min of supine recovery. Hemodynamic and autonomic responses (assessed via heart rate variability, HRV) were measured before-, during-, and after-LBNP application using Task Force Monitor® (CNSystems, Graz, Austria). Blood was also collected to measure estrogen and progesterone levels.

Results

In this companion paper, we have exclusively assessed 14 females from the previous study (Shankwar et al., 2023): 8 in the follicular phase of the menstrual cycle (mean age 23.38 ± 3.58 years, height 166.00 ± 5.78 cm, weight 57.63 ± 5.39 kg and BMI of 20.92 ± 1.96 25 kg/m2) and 6 in the luteal phase (mean age 22.17 ± 1.33 years, height 169.83 ± 5.53 cm, weight 62.00 ± 7.54 kg and BMI of 21.45 ± 2.63 kg/m2). Baseline estrogen levels were significantly different from the follicular phase as compared to the luteal phase: (33.59 pg/ml, 108.02 pg/ml, respectively, p < 0.01). Resting hemodynamic variables showed no difference across the menstrual phases. However, females in the follicular phase showed significantly lower resting values of low-frequency (LF) band power (41.38 ± 11.75 n.u. and 58.47 ± 14.37 n.u., p = 0.01), but higher resting values of high frequency (HF) band power (58.62 ± 11.75 n.u. and 41.53 ± 14.37 n.u., p = 0.01), as compared to females in the luteal phase. During hypovolemia, the LF and HF band powers changed only in the follicular phase F(1, 7) = 77.34, p < 0.0001 and F(1, 7) = 520.06, p < 0.0001, respectively.

Conclusions

The menstrual phase had an influence on resting autonomic variables, with higher sympathetic activity being observed during the luteal phase. Central hypovolemia leads to increased cardiovascular and autonomic responses, particularly during the luteal phase of the menstrual cycle, likely due to higher estrogen levels and increased sympathetic activity.

Association of gender with cardiovascular and autonomic responses to central hypovolemia

Introduction

Lower body negative pressure (LBNP) eliminates the impact of weight-bearing muscles on venous return, as well as the vestibular component of cardiovascular and autonomic responses. We evaluated the hemodynamic and autonomic responses to central hypovolemia, induced by LBNP in both males and females.

Methodology

A total of 44 participants recruited in the study. However, 9 participants did not complete the study protocol. Data from the remaining 35 participants were analysed, 18 males (25.28 ± 3.61 years, 181.50 ± 7.43 cm height, 74.22 ± 9.16 kg weight) and 17 females (22.41 ± 2.73 years, 167.41 ± 6.29 cm height, 59.06 ± 6.91 kg weight). During the experimental protocol, participants underwent three phases, which included 30 min of supine rest, four 4 min intervals of stepwise increases in LBNP from -10 mmHg to -40 mmHg, and 5 min of supine recovery. Throughout the protocol, hemodynamic variables such as blood pressure, heart rate, stroke index, cardiac index, and total peripheral resistance index were continuously monitored. Autonomic variables were calculated from heart rate variability measures, using low and high-frequency spectra, as indicators of sympathetic and parasympathetic activity, respectively.

Results

At rest, males exhibited higher systolic (118.56 ± 9.59 mmHg and 110.03 ± 10.88 mmHg, p < 0.05) and mean arterial (89.70 ± 6.86 and 82.65 ± 9.78, p < 0.05) blood pressure as compared to females. Different levels of LBNP altered hemodynamic variables in both males and females: heart rate [F(1,16) = 677.46, p < 0.001], [F(1,16) = 550.87, p < 0.001]; systolic blood pressures [F(1,14) = 3,186.77, p < 0.001], [F(1,17) = 1,345.61, p < 0.001]; diastolic blood pressure [F(1,16) = 1,669.458, p < 0.001], [F(1,16) = 1,127.656, p < 0.001]; mean arterial pressures [F(1,16) = 2,330.44, p < 0.001], [F(1,16) = 1,815.68, p < 0.001], respectively. The increment in heart rates during LBNP was significantly different between both males and females (p = 0.025). The low and high-frequency powers were significantly different for males and females (p = 0.002 and p = 0.001, respectively), with the females having a higher increase in low-frequency spectral power.

Conclusions and future directions

Cardiovascular activity and autonomic function at rest are influenced by gender. During LBNP application, hemodynamic and autonomic responses differed between genders. These gender-based differences in responses during central hypovolemia could potentially be attributed to the lower sympathetic activity in females. With an increasing number of female crew members in space missions, it is important to understand the role sex-steroid hormones play in the regulation of cardiovascular and autonomic activity, at rest and during LBNP.

Developing a "dry lab" activity using lower body negative pressure to teach physiology

In this paper we assessed how lower body negative pressure (LBNP) can be used to teach students the physiological effects of central hypovolemia in the absence of the LBNP and/or a medical monitor using a "dry lab" activity using LBNP data that have been previously collected. This activity was performed using published LBNP papers, with which students could explore LBNP as an important tool to study physiological responses to central hypovolemia as well as consider issues in performing an LBNP experiment and interpreting experimental results. The activity was performed at the All India Institute of Medical Sciences, New Delhi, with 31 graduate students and 4 teachers of physiology. Both students and teachers were provided with a set of questionnaires that inquired about aspects related to the structure of the activity and how this activity integrated research and knowledge, as well as aspects related to motivation of the students and teachers to perform the activity. Our results from student and teacher surveys suggest that a "dry lab" activity using LBNP to teach physiology can be an important tool to expose students to the basics of systems physiology as well as to provide useful insights into how research is performed. Providing insight into research includes formulating a research question and then designing (including taking into account confounding variables), implementing, conducting, and interpreting research studies. Finally, developing such an activity using LBNP can also serve as a basis for developing research capacities and interests of students even early in their medical studies.

Effect of Vibrotherapy on Body Fatness, Blood Parameters and Fibrinogen Concentration in Elderly Men

Elderly people need activities that will positively contribute to a satisfactory process of getting older. Vibration training uses mechanical stimulus of a vibrational character that, similarly to other forms of physical activity, affects metabolic processes and conditions of health. The aim of this work was to assess the influence of thirty vibration treatments on body fatness, hematologic and rheologic indexes of blood, and proteinogram and fibrinogen concentration in elderly men’s blood. The study included twenty-one males, aged 60–70 years (mean age 65.3 ± 2.7), who were randomly assigned into a vibrotherapy group (VG) and took part in interventions on mattresses generating oscillatory-cycloid vibrations, and a control group (CG), without interventions. In all patients the following assessments were performed twice: an assessment of body fatness using the bioimpedance method, a complete blood count with a hematology analyzer, and erythrocyte aggregation by a laser-optical rotational cell analyzer; whereas, total plasma protein and fibrinogen values were established, respectively, by biuret and spectrophotometric methods. In order to compare the impact of vibrotherapy on changes in the analyzed variables, analysis of variance (ANOVA) or the Wilcoxon test were used. After applying thirty vibration treatments in the VG, a significant decrease in body fatness parameters was confirmed: BM (∆BM: −2.7 ± 2.0; p = 0.002), BMI (∆BMI: −0.9 ± 0.7; p = 0.002), BF (∆BF: −2.5 ± 2.5; p = 0.013), and %BF (∆%BF: −2.0 ± 2.7; p = 0.041), as well as in RBC (∆RBC: −0.1 ± 0.1; p = 0.035). However, changes in erythrocyte aggregation and proteinogram were not confirmed. It was found that after thirty treatments with VG, a significant decrease of fibrinogen level took place (∆ = −0.3 ± 0.3, p = 0.005). Application of thirty vibrotherapy treatments positively affected body fatness parameters and fibrinogen concentrations in the examined. However, further research should include a greater number of participants.