Background: As the COVID-19 pandemic continues, determining hospital demands has become a vital priority. Heart rate variability (HRV) has been linked to both the presence of viral infection and its severity. We investigate the possibility of using HRV parameters in comparison to other clinical parameters for predicting the hospital length of stay (LOS) for COVID-19 patients. Methods: This was a population-based cohort study. Measurements were performed in a specialized hospital for respiratory disease, dedicated to COVID-19. Patients were polymerase chain reaction positive for COVID-19 and on their 1 st day of admission. Heart period, respiratory sinus arrhythmia (RSA), low frequency (LF) HRV, and vagal efficiency were calculated from electrocardiogram signals. This study investigated the correlation of HRV, demographic, and laboratory parameters with hospital LOS. Results: Forty-one participants were recruited, with a significant relationship, observed between hospital LOS and some demographic and clinical parameters such as lymphocyte count, age, and oxygen saturation of arterial blood. There was a negative relationship between LF and hospital LOS ( r = −0.53, 95% confidence interval: −0.73, −0.24). Higher vagal efficiency predicted shorter hospital LOS in patients younger than 40 years of age (19.27% shorter hospital LOS was associated with a one SD higher value of VE, P = 0.007). Conclusion: HRV measurement is a non-invasive, inexpensive, and scalable procedure that produces several metrics, some of which are useful for predicting hospital LOS and managing treatment resources during COVID-19 pandemic.

Background The activity of autonomic nervous system and its association with organ damage have not been entirely elucidated in hemorrhagic shock. The aim of this study was to investigate heart rate variability (HRV) and pulmonary gas exchange in hemorrhagic shock during unilateral subdiaphragmatic vagotomy. Methods Male Sprague Dawley rats were randomly assigned into groups of Sham, vagotomized (Vag), hemorrhagic shock (HS) and Vag + HS. HS was induced in conscious animals by blood withdrawal until reaching to mean arterial blood pressure (MAP) of 40 ± 5 mmHg. Then, it was allowed to MAP returning toward the basal values. MAP and heart rate (HR) were recorded throughout the experiments, HRV components of low (LF, sympathetic index), high (LH, parasympathetic index), and very low (VLF, injury index) frequencies and the LF/HF ratio calculated, and the lung histological and blood gas parameters assessed. Results In the initial phases of HS, the increase in HR with no change in MAP were observed in both HS and Vag + HS groups, while LF increased only in the HS group. In the second phase, HR and MAP decreased sharply in the HS group, whereas, only MAP decreased in the Vag + HS group. Meanwhile, LF and HF increased relative to their baselines in the HS and Vag + HS groups, even though the values were much pronounced in the HS group. In the third phase, HR, MAP, LF, HF, and the LF/HF ratio were returned back to their baselines in both HS and Vag + HS groups. In the Vag + HS group, the VLF was lower and HR was higher than those in the other groups. Furthermore, blood gas parameters and lung histology indicated the impairment of gas exchange in the Vag + HS group. Conclusions The sympathetic activity is predominant in the first phase, whereas the parasympathetic activity is dominant in the second and third phases of hemorrhagic shock. There is an inverse relationship between the level of VLF and lung injury in vagotomized animals subjected to hemorrhagic shock.

The nTS is the first site of integration and processing of sensory afferent information and is one of the crucial brainstem nuclei involved in cardiorespiratory reflexes. This nucleus receives afferent information from many visceral structures in the thorax and abdomen via the peripheral branches of the vagus nerve. Vagal afferents release glutamate (Glu) which initiates signaling processes that leads to chemo- and baroreflex-mediated changes in sympathetic and phrenic nerve activity. Previous studies by us have shown that decreasing afferent input via unilateral vagotomy augmented nTS astrocyte complexity. Astrocytes contribute to regulation of Glu concentration by removing Glu from the synaptic cleft via excitatory amino acid transporters (EAATs). We hypothesized that vagotomy attenuates Glu signaling in the nTS due to increased Glu uptake by greater EAAT expression or function. Surgical transection or sham surgery of the right cervical vagus nerve caudal to the nodose ganglion was performed in male Sprague-Dawley rats. One week after surgery, mean arterial pressure (MAP), heart rate (HR), and splanchnic sympathetic and phrenic nerve activity (SSNA and PhrNA) were recorded in anesthetized and ventilated rats. Intact vagus nerves and the right phrenic nerve were acutely transected. Nanoinjections of Glu (30 nl, 1-10 mM) into the nTS decreased MAP, HR, SSNA and PhNA in both sham and vagotomy groups. Vagotomy blunted the HR, SSNA and PhrNA responses, indicating that Glu signaling was attenuated. To determine if increased EAAT function contributed to blunted Glu responses, the EAAT blocker TFB-TBOA (10nM, 60nl) was nanoinjected into the nTS. EAAT blockade mimicked the effect of Glu, producing similar depressor, bradycardic, and apneic responses in both groups. TBOA also enhanced the cardiorespiratory responses to Glu injection in both groups. EAAT blockade did not restore Glu responses in the vagotomy group compared to sham. Taken together, these data suggest that increased EAAT function did not account for the attenuated Glu signaling in the nTS. Further studies are needed to uncover the mechanisms by which vagotomy affects Glu signaling in the nTS. NIH R01 HL098602 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Introduction: The activity of autonomic nervous system and its association with organ damage have not been entirely elucidated in hemorrhagic shock. The aim of this study was to investigate heart rate variability (HRV) and pulmonary gas exchange in hemorrhagic shock during unilateral subdiaphragmatic vagotomy. Methods: Male Sprague Dawley rats were randomly assigned into groups of sham, vagotomized (Vag), HS and Vag+HS. HS was induced in conscious animals by blood withdrawal until reaching to mean arterial blood pressure (MAP) of 40±5 mm Hg. Then, it was allowed to MAP returning toward the basal values. MAP and heart rate (HR) were recorded throughout the experiments, HRV components of low (LF, sympathetic index), high (LH, parasympathetic index), and very low (VLF, injury index) frequencies and the LF/HF ratio (sympathetic index) calculated, and the lung histological and blood gas parameters assessed. Results: In the initial phases of HS, the increase in HR with no change in MAP were observed in both HS and Vag+HS groups, while LF increased only in the HS group. In the second phase, HR and MAP decreased sharply in the HS group, whereas, MAP decreased only in the Vag+HS group. Meanwhile, LF and HF increased relative to their baselines in the HS and Vag+HS groups, even though the values were much pronounced in the HS group. In the third phase, HR, MAP, LF, HF, and the LF/HF ratio were returned back to their baselines in both HS and Vag+HS groups. However, in the Vag+HS group, the VLF was lower and HR was higher than those in the other groups. Furthermore, blood gas parameters and lung histology indicated the impairment of gas exchange in the Vag+HS group. Conclusions : The sympathetic activity is predominant in the first phase, whereas the parasympathetic activity is dominant in the second and third phases of hemorrhagic shock. Furthermore, hemorrhagic shock with vagotomy may be linked to lung injury and decreased VLF.

No abstract