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This study aimed to determine the influence of intermittent hypoxia and the days required for a worker to be acclimatized in high-altitude countries. We conducted an experimental study. Ten nonsmoking male students were randomly recruited from King Saud University. Fourteen days of exposure to intermittent normobaric hypoxia (15%) was the independent variable. Heart rate (HR), respiratory frequency (RF), minute ventilation (VE), respiratory exchange ratio (RER), tidal volume (VT), oxygen uptake (VO2),VO2/kg, VO2/HR, VE/VO2, and VE/VCO2 were the dependent variables. Our results showed that 12 days of exposure to intermittent hypoxia were sufficient for workers to acclimatize to hypoxia based on their respiratory responses (i.e., HR, RF, VE). This type of acclimatization session is very important for workers who are suddenly required to work in such an environment, because prolonged exposure to high altitude without acclimatization leads to cell death due to a lack of oxygen, and this, in turn, puts workers' lives at risk. [ABSTRACT FROM AUTHOR]

Offering large muscle benefits despite low metabolic demand, continuous eccentric exercise appears to be an interesting alternative to concentric exercise. Nevertheless, further knowledge is needed about prolonged eccentric exercise. This work sought to investigate the cardiovascular responses to prolonged constant-load eccentric compared to concentric cycling. Ten healthy males performed two 45-min exercise sessions of either concentric or eccentric cycling separated by a month and matched for heart rate during the first 5 min of exercise. Cardiorespiratory, autonomic nervous system and vascular responses were assessed at rest, and during exercise and recovery. During cycling, oxygen uptake, cardiac output and systolic blood pressure were similar but heart rate and diastolic blood pressure were greater whereas stroke volume was lower during eccentric than concentric cycling (118±21 vs. 104±10 bpm; 77±9 vs. 65±8 mmHg; 122±12 vs. 135±13 mL). Baroreflex and noradrenaline concentration were altered during eccentric cycling, and after eccentric exercise, vascular tone was greater than after concentric cycling. We observed increased cardiovascular strain and altered baroreflex activity during eccentric compared with concentric exercise, suggesting eccentric cycling triggers greater sympathetic activity. [ABSTRACT FROM AUTHOR]

Recent studies have demonstrated that a mild stimulation of the dorsomedian nucleus of the hypothalamus (DMH), a defense area, induces the inhibition of the carotid chemoreflex tachypnea. DMH activation reduces the cardiac chemoreflex response via the dorsolateral part of the periaqueductal grey matter (dlPAG) and serotonin receptors (5-HT 3 subtype) in the nucleus tractus solitarius (NTS). The objectives of this study were to assess whether dlPAG and subsequent NTS 5-HT 3 receptors are involved in chemoreflex tachypnea inhibition during mild activation of the DMH. For this purpose, peripheral chemoreflex was activated with potassium cyanide (KCN, 40 μg/rat, i.v.) during electrical and chemical minimal supra-threshold (mild) stimulation of the dlPAG or DMH. In both situations, changes in respiratory frequency (RF) following KCN administration were reduced. Moreover, pharmacological blockade of the dlPAG prevented DMH-induced KCN tachypnea inhibition. Activation of NTS 5-HT 3 receptors also reduced chemoreflex tachypnea in a dose-dependent manner. In addition, blockade of NTS 5-HT 3 receptors with granisetron (2.5 but not 1.25 mM), or the use of mice lacking the 5-HT 3a receptor (5-HT 3a KO), prevented dlPAG-induced KCN reductions in RF. A respiratory hypothalamo-midbrain-medullary pathway (HMM) therefore plays a crucial role in the inhibition of the hyperventilatory response to carotid chemoreflex. [ABSTRACT FROM AUTHOR]

We developed a periodic hypobaric hypoxic environment (PHHE) system. Characteristics of this system varied between decreased pressure at an altitude of 1,500 m for 180 seconds and increased pressure at an altitude of 0 m for 180 seconds. The present study aimed to determine the effects of PHHE on physiological responses during endurance exercise and recovery after exercise. This study included 12 healthy men, and they provided written informed consent. All subjects performed a cycling exercise for 30 minutes and recovered after exercise for 10 minutes. The exercise protocol was performed with 20% maximum oxygen uptake for 6 minutes (warm-up), 40 % for 18 minutes (main exercise), and 20 % for 6 minutes (cool down). We established two experimental conditions: exercise with the PHHE and the control (C). The C condition involved exercise using the PHHE at an altitude of 0 m, and the atmospheric pressure was not changed. In the PHHE condition, the atmospheric pressure was changed periodically from 967 to 817 hPa (the external pressure was 1,008 hPa). Subjects' heart rate (HR), blood pressure (BP), arterial oxygen saturation (SpO2), rating of perceived exertion, and respiratory responses were measured in both conditions. The SpO2, HR and systolic BP during exercise were significantly lower in the PHHE condition than in the C condition. The HR post-exercise was significantly lower. After exercise, the ln HF, an index of cardiac parasympathetic nervous system modulation, was significantly higher. In conclusion, during endurance exercise, cardiocirculatory responses in the PHHE condition were decreased. [ABSTRACT FROM AUTHOR]

Using an opto-cardiograph combined with an infrared gas analyzer regular bouts of abdominal contractions were recorded from last instar larva of Bombus terrestris. The rate of CO2 release was about 0.7 ml g-1 h-1. The bouts of contractions were of two types: weak extracardiac pulsations and vigorous pumping. The frequencies of pulsations and pumping were 25-35 per min and 8-12 per min, respectively. Bouts of extracardiac pulsations and abdominal pumping were independent of each other and sometimes overlapped. Cardiac contractions (heartbeats) were continuous (57-63 pulses/min). This study suggests that the periodically occurring abdominal contractions play an essential role in respiration and/or in haemolymph circulation in larvae of B. terrestris.

Highlights: [•] Effects of inorganic mercury through trophic and waterborne exposure. [•] Hg impairment of cardiorespiratory responses to graded hypoxia. [•] Effects of mercury, via water or diet, on metabolic rate, gill ventilation, respiratory frequency and O2 extraction by gills. [•] Hg induces decrease in the heart rate and increase on critical oxygen tensions. [•] Two species Brazilian fish ecologically distinct, matrinxã (Brycon amazonicus) and traíra (Hoplias malabaricus). [ABSTRACT FROM AUTHOR]

Horses are elite athletes when compared with other mammalian species. In the latter, performance is limited by cardiovascular or musculoskeletal performance whereas in athletic horses it is the respiratory system that appears to be rate limiting and virtually all horses exercising at high intensities become hypoxaemic and hypercapnoeic. This is due to both diffusion limitation and a level of ventilation inadequate for the metabolic level that enables horses to exercise at these intensities. In conjunction with these blood gas changes, total pulmonary resistance increases and the work of breathing rises exponentially and airflow eventually plateaus despite increases in inspiratory and expiratory intrapleural pressures. Horses breathe at comparatively high frequencies when galloping due to the tight 1:1 coupling of strides to breathing. Whether this effects gas exchange and, if so, to what extent, has not been fully elucidated. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the influence of backpacks carriage with different weights on some physiological functions in 12.5-year-old male students. Fifteen volunteers (height: 163±1.7cm, and weight: 51±1.4kg) were selected to carry school backpacks of 8, 10.5, and 13 % of their own body weights on a treadmill at the 3.9 km.h-1 for 15 mm, were 0% body weight was used as control. Respiratory frequency (RF), minute ventilation (Mv), heart rate (HR), energy expenditure (EE), and oxygen consumption (VO2) of subjects were measured by Gas Analyzer System, in each of the carriage tests, in 3 situations: rest, exercise (15 mm walking) and recovery (3 mm after walking). The Repeated-measures ANOVA and paired t-test were used for statistical analysis of data in significant level of p ⩽0.05. The results indicated that the MV, EE and VO2 during and 3 mm after carrying backpacks equal to 10.5 and 13% of body weight were significantly higher than in 0 & 8% of body weight load conditions (p<0.025). No significant differences were found in RF and HR values among different load conditions (p>0.05). Walking with backpack equal to 8% of body weight did not significantly change physiological parameters (p>0.05). Thus, the weight of backpack for high school students can be recommended as 8% of their body weight. [ABSTRACT FROM AUTHOR]

The effect of chloride cell proliferation on the respiratory function was evaluated by measuring oxygen consumption (V O2) and ventilatory parameters during normoxia and gradual hypoxia in the tropical fish Hoplias malabaricus. Chloride cell proliferation was induced by keeping fish in deionized water, and the effect on the respiratory function was measured on the 1st, 2nd, and 7th day in this water using a flow-through respirometry system. Plasma osmolarity and the partial pressure of arterial oxygen (PaO2) and carbon dioxide (PaCO2) were measured under conditions of normoxia and severe hypoxia. Chloride cell proliferation on the lamellae significantly increased the water-blood diffusion distance on the 2nd and 7th day in deionized water.VO2 was kept constant until the critical oxygen pressure (PcO2) of 21.6±0.9 mmHg in both the control and deionized water fish was reached. The ventilatory parameters were higher in deionized water fish in normoxia, and increased during hypoxia, matching decreases in the water's partial O2 pressure. Impairment of the respiratory function was evidenced by the decrease of PaO2 of deionized water fish in normoxic condition. However, despite the changes in the epithelial morphology of gills in fish kept in deionized water, H. malabaricus proved be a hypoxic-tolerant tropical species. oxygen partial pressure ·PcO2 critical oxygen pressure ·PeO2 expired water from opercular cavity ·PinO2 oxygen tension of ingoing water of the respirometer · PiO2 inspired water from buccal cavity &middot PoutO2 oxygen tension of outgoing water of the respirometer · PwO2 partial oxygen pressure · τh water-blood barrier thickness · VO2 oxygen consumption · VG gill ventilation ·VT ventilatory tidal volume. [ABSTRACT FROM AUTHOR]

Recent observations from our group seem to indicate that repeated stress-evoked dorsomedian hypothalamic nucleus (DMH) activation in rats can lead to persistent bradypnea. One possibility was that respiratory responses to peripheral chemoreceptor activation were reduced by DMH stimulation. In the present study, we therefore investigated the effect of minimal supra-threshold DMH stimulation on respiratory carotid chemoreflex responses. For this purpose, the chemoreflex was activated by potassium cyanide (KCN, 40μg/rat, i.v.) during electrical and chemical stimulation of the DMH. In both situations, changes in breathing frequency but not tidal volume responses to KCN administration were reduced. These findings suggest that low DMH neurotransmission negatively affects respiratory chemoreflex responses and may be involved in stress-induced bradypnea., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Background. The aim of this study was to investigate the effect of stroop test on respiratory responses and heart rate (HR) before and during exercise. Methods. Twelve healthy normotensive males performed the following three experimental tasks in a random fashion; (1) paying attention to exercise task before and during exercise (C), (2) paying attention to stroop test before and during exercise (ST), (3) resting condition. Borg scale, exercise time, HR and respiratory variables such as minute ventilation, tidal volume, respiratory rate, and oxygen consumption were continuously measured for 6 min prior to exercise and during exercise for all experimental conditions. Exercise test was conducted at 100% of the maximal work rate and was performed until voluntary fatigue. Results. C condition had significantly higher level of HR response than ST condition prior to exercise (p<0.05). C condition also had significantly lower level of respiratory rate than ST condition immediately after beginning exercise (p<0.05). On the other hand, no significant differences were found for the other variables between C and ST conditions. Conclusions. These findings suggested that stroop test can be depressed anticipatory HR response before the start of exercise and ventilator efficiency immediately after exercise. [ABSTRACT FROM AUTHOR]

Background: During preparation and draping of periorbital area, neck flexion causes displacement of the endotracheal tube tip toward the carina. Stimulation of the tracheal mucosa may cause bucking, increased intraocular pressure (IOP), laryngospasm, bronchospasm, change in end-tidal carbon dioxide pressure (PETCO2) or peripheral arterial haemoglobin oxygen saturation (SpaO2) during light anaesthesia., Objective: To investigate the influence of head and neck flexion after endotracheal intubation on heart rate (HR), systolic and diastolic blood pressure (SAP and DAP), SpaO2, PETCO2 and IOP in patients undergoing cataract surgery during general anesthesia., Method: In this prospective observational study, 106 ASA physical status I and II patients scheduled for elective cataract surgery under general anaesthesia were studied. Anaesthesia was induced with thiopental sodium, lidocaine and fentanyl. Atracurium 0.5 mg/kg was given to facilitate tracheal intubation. HR, SAP, DAP, SpaO2, PETCO2, and IOP were measured at 1, 2, and 5 minutes after head flexion., Results: Mean SAP, DAP, IOP, and HR were significantly increased after head flexion compared with baseline values (P < 0.05). PETCO2 and SpaO2 were significantly decreased at 1 and 2 minutes after head flexion compared with baseline values (P < 0.001)., Conclusion: It is concluded that endotracheal tube movement by changes in head and neck position has significant effects on heart rate, systolic and diastolic blood pressures, laryngeal reflexes, SpaO2, PETCO2, and intraocular pressure in patients undergoing cataract surgery under general anaesthesia.