The pathophysiological mechanisms underlining constipation are incompletely understood, but prolonged bed rest is commonly considered a relevant determinant.
Our primary aim was to study the effect ...of long-term physical inactivity on determining a new onset of constipation. Secondary aim were the evaluation of changes in stool frequency, bowel function and symptoms induced by this prolonged physical inactivity.
Ten healthy men underwent a 7-day run-in followed by 35-day study of experimentally-controlled bed rest. The study was sponsored by the Italian Space Agency. The onset of constipation was evaluated according to Rome III criteria for functional constipation. Abdominal bloating, flatulence, pain and urgency were assessed by a 100mm Visual Analog Scales and bowel function by adjectival scales (Bristol Stool Form Scale, ease of passage of stool and sense of incomplete evacuation). Daily measurements of bowel movements was summarized on a weekly score. Pre and post bed rest Quality of Life (SF-36), general health (Goldberg's General Health) and depression mood (Zung scale) questionnaires were administered.
New onset of functional constipation fulfilling Rome III criteria was found in 60% (6/10) of participants (p=0.03). The score of flatulence significantly increased whilst the stool frequency significantly decreased during the week-by-week comparisons period (repeated-measures ANOVA, p=0.02 and p=0.001, respectively). Stool consistency and bowel symptoms were not influenced by prolonged physical inactivity. In addition, no significant changes were observed in general health, in mood state and in quality of life at the end of bed rest.
Our results provide evidence that prolonged physical inactivity is relevant etiology in functional constipation in healthy individuals. The common clinical suggestion of early mobilization in bedridden patients is supported as well.
New Findings
What is the central question of this study?
Astronauts on‐board the International Space Station (ISS) perform daily exercises designed to prevent muscle atrophy and bone ...demineralization: what is the effect of resistive exercise performed by subjects while exposed to the same level of hypercapnia as on the ISS on intraocular pressure (IOP)?
What is the main finding and its importance?
The static exercise‐induced elevation in IOP during 6° prone head‐down tilt (simulating the headward shift of body fluids in microgravity) is augmented by hypercapnia and exceeds the ocular hypertension threshold.
The present study assessed the effect of 6° head‐down (establishing the cephalad fluid displacement noted in astronauts in microgravity) prone (simulating the effect on the eye) tilt during rest and exercise (simulating exercise performed by astronauts to mitigate the sarcopenia induced by unloading of weight‐bearing limbs), in normocapnic and hypercapnic conditions (the latter simulating conditions on the International Space Station) on intraocular pressure (IOP). Volunteers (mean age = 57.8 ± 6 years, n = 10) participated in two experimental sessions, each comprising: (i) 10 min rest, (ii) 3 min static handgrip exercise (30% max), and (iii) 2 min recovery, inspiring either room air (NCAP) or a hypercapnic mixture (1% CO2, HCAP). We measured IOP in the right eye, cardiac output (CO), stroke volume (SV), heart rate (HR) and mean arterial pressure (MAP) at regular intervals. Baseline IOP in the upright seated position while breathing room air was 14.1 ± 2.9 mmHg. Prone 6° head‐down tilt significantly (P < 0.01) elevated IOP in all three phases of the NCAP (rest: 27.0 ± 3.7 mmHg; exercise: 32.2 ± 4.8 mmHg; recovery: 27.4 ± 4.0 mmHg) and HCAP (rest: 27.3 ± 4.3 mmHg; exercise: 34.2 ± 6.0 mmHg; recovery: 29.1 ± 5.8 mmHg) trials, with hypercapnia augmenting the exercise‐induced elevation in IOP (P < 0.01). CO, SV, HR and MAP were significantly increased during handgrip dynamometry, but there was no effect of hypercapnia. The observed IOP measured during prone 6° HDT in all phases of the NCAP and HCAP trials exceeded the threshold pressure defining ocular hypertension. The exercise‐induced increase in IOP is exacerbated by hypercapnia.
New Findings
What is the central question of this study?
Do females and males exhibit a similar sarcopenic response as a consequence of normoxic and hypoxic bed rest?
What is the main finding and its ...importance?
During 10‐day bed rest, exposure to a simulated (normobaric hypoxia) altitude of ∼4000 m does not exert additional significant structural or functional effect on the weight‐bearing muscles in females compared to those noted under normoxic conditions. Whereas males and females exhibit decrements in muscle cross‐sectional area and mass during normoxic and hypoxic bed rest, a concomitant strength decrement was only observed in males.
This study investigated the effects of hypoxia on the known processes of adaptation of body composition and muscle function to normoxic inactivity. Females (n = 12) and males (n = 11) took part in the following interventions: hypoxic ambulation (HAMB; ∼4000 m); hypoxic bed rest (HBR; ∼4000 m) and normoxic bed rest (NBR). Prior to and immediately following each intervention, body composition, thigh and lower leg cross‐sectional area (CSA) and isometric muscular strength were recorded. Participants lost body mass (HAMB: male −1.5 ± 0.9 kg, female −1.9 ± 0.7 kg; HBR: male −2.0 ± 1.8 kg, female −2.4 ± 0.8 kg; NBR: male −1.4 ± 1.3 kg, female −1.4 ± 0.9 kg) and lean mass (HAMB: male −3.9 ± 3.0%, female −3.4 ± 2.0%; HBR: male −4.0 ± 4.4%, female −4.1 ± 2.0%; NBR: male −4.0 ± 3.4%, female −2.2 ± 2.7%) with no between‐condition or sex differences. Knee extension decreased for males in NBR compared to HAMB (HAMB: male −0.2 ± 9.1%, female 1.3 ± 4.9%; HBR: male −7.8 ± 10.3%, female −3.3 ± 10.9%; NBR: male −14.5 ± 11%, female −3.4 ± 6.9%). Loss of force during maximal voluntary contraction (MVC) in the knee extensors was significantly different between males and females following NBR. There were no other significant changes noted following the experimental interventions. There were no differences recorded between sexes in maximal MVC for elbow or ankle joints. Female lower leg CSA decreased following bed rest (HAMB: ‐4.5 ± 2.0%; HBR: ‐9.9 ± 2.6%; NBR: ‐8.0 ± 1.6%). These findings indicate that a 10‐day hypoxic bed rest does not exert any significant additional effect on muscle atrophy when compared to NBR, except for female thigh CSA. In contrast to males, who exhibited a significant loss of muscle strength, no such decrement in strength was observed in the female participants.
Our understanding of skeletal muscle structural and functional alterations during unloading has increased in recent decades, yet the molecular mechanisms underpinning these changes have only started ...to be unraveled. The purpose of the current investigation was to assess changes in skeletal muscle gene expression after 21 days of bed rest, with a particular focus on predicting upstream regulators of muscle disuse. Additionally, the association between differential microRNA expression and the transcriptome signature of bed rest were investigated. mRNAs from musculus vastus lateralis biopsies obtained from 12 men before and after the bed rest were analyzed using a microarray. There were 54 significantly upregulated probesets after bed rest, whereas 103 probesets were downregulated (false discovery rate 10%; fold-change cutoff ≥1.5). Among the upregulated genes, transcripts related to denervation-induced alterations in skeletal muscle were identified, e.g., acetylcholine receptor subunit delta and perinatal myosin. The most downregulated transcripts were functionally enriched for mitochondrial genes and genes involved in mitochondrial biogenesis, followed by a large number of contractile fiber components. Upstream regulator analysis identified a robust inhibition of the myocyte enhancer factor-2 (MEF2) family, in particular MEF2C, which was suggested to act upstream of several key downregulated genes, most notably peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α)/peroxisome proliferator-activated receptors (PPARs) and CRSP3. Only a few microRNAs were identified as playing a role in the overall transcriptome picture induced by sustained bed rest. Our results suggest that the MEF2 family is a key regulator underlying the transcriptional signature of bed rest and, hence, ultimately also skeletal muscle alterations induced by systemic unloading in humans.
The eye in extreme environments Jaki Mekjavic, Polona; Tipton, Michael J.; Mekjavic, Igor B
Experimental physiology,
1 January 2021, 2021-01-00, 20210101, Letnik:
106, Številka:
1
Journal Article
Recenzirano
Odprti dostop
New Findings
What is the topic of this review?
This review describes the effect of extreme environments on the visual system.
What advances does it highlight?
The review highlights the way in which ...environmental stressors affect the eye and vision, both directly and indirectly.
Much is known about the physiology and anatomy of the eye. Much less is known about the impact of different environments on the eye, and yet it is the pathophysiology that results from this interaction that is often the precursor to disaster. The present review focuses on the effect of different extreme environments on the visual system; in particular, the way in which such environments affect the sensory mechanism of that system.
Abstract Introduction Skin regions differ in their sensitivity to temperature stimuli. The present study examined whether such regional differences were also evident in the perception of thermal ...comfort. Methods Regional thermal comfort was assessed in males ( N = 8) and females ( N = 8), by having them regulate the temperature of the water delivered to a water-perfused suit (WPS), within a temperature range considered thermally comfortable. In separate trials, subjects regulated the temperature of the WPS, or specific regions of the suit covering different skin areas (arms, legs, front torso and back torso). In the absence of subjective temperature regulation (TR), the temperature changed in a sinusoidal manner from 10 °C to 50 °C; by depressing a switch and reversing the direction of the temperature at the limits of the thermal comfort zone (TCZ), each subject defined TCZ for each body region investigated. Results The range of regulated temperatures did not differ between genders and skin regions. Local Tsk at the lower and upper limits of the TCZ was similar for both genders. Higher ( p < 0.05) local Tsk was preferred for the arms (35.4 ± 2.1 °C), compared to other regions (legs: 34.4 ± 5.4 °C, front torso: 34.6 ± 2.8 °C, 34.3 ± 6.6 °C), irrespective of gender. Conclusions In thermally comfortable conditions, the well-established regional differences in thermosensitivity are not reflected in the TCZ, with similar temperature preferences by both genders. Thermal comfort of different skin regions and overall body is not achieved at a single skin temperature, but at range of temperatures, defined as the TCZ.
The present study compared the thermal comfort zones (TCZ) of the hands, feet and head in eight male and eight female participants, assessed with water-perfused segments (WPS).
On separate occasions, ...and separated by a minimum of one day, participants were requested to regulate the temperature of three distal skin regions (hands, feet and head) within their TCZ. On each occasion they donned a specific water-perfused segment (WPS), either gloves, socks or hood for assessing the TCZ of the hands, feet and head, respectively. In the absence of regulation, the temperature of the water perfusing the WPS changed in a saw-tooth manner from 10 to 50°C; by depressing a switch and reversing the direction of the temperature at the limits of the TCZ, each participant defined the TCZ for each skin region investigated.
The range of regulated temperatures (upper and lower limits of the TCZ) did not differ between studied skin regions or between genders. Participants however maintained higher head (35.7±0.4°C; p˂0.001) skin temperature (Tsk) compared to hands (34.5±0.8°C) and feet (33.8±1.1°C).
When exposed to normothermic conditions, distal skin regions do not differ in ranges of temperatures, perceived as thermally comfortable.
•Regional thermal comfort and the effect of gender•Temperature regulation within the water perfused suit•Determination of the thermal comfort zone•No difference in the thermal comfort zone between males and females
Acclima(tiza)tion to heat or hypoxia enhances work capacity in hot and hypoxic environmental conditions, respectively; an acclimation response is considered to be mediated by stimuli-specific ...molecular/systemic adaptations and potentially facilitated by the addition of exercise sessions. Promising findings at the cellular level provided the impetus for recent studies investigating whether acclimation to one stressor will ultimately facilitate whole body performance when exercise is undertaken in a different environmental condition. The present critical Mini-Review examines the theory of cross-adaptation between heat and hypoxia with particular reference to the determinants of aerobic performance. Indeed, early functional adaptations (improved exercise economy and enhanced oxyhemoglobin saturation) succeeded by later morphological adaptations (increased hemoglobin mass) might aid acclimatized humans perform aerobic work in an alternative environmental setting. Longer-term acclimation protocols that focus on the specific adaptation kinetics (and further allow for the adaptation reversal) will elucidate the exact physiological mechanisms that might mediate gains in aerobic performance or explain the lack thereof.
The present study tested the hypothesis that at any given ambient temperature (Ta), thermal comfort (TC) is not only a function of the temperature per se, but is also influenced by the temperatures ...rate of change and direction.
Twelve healthy young (age: 23 ± 3) male participants completed experimental trials where Ta increased from 15° to 40 °C (heating) and then decreased from 40 to 15 °C (cooling). In one trial (FAST), the rate of change in Ta was maintained at 1 °C.min−1, and in the other (SLOW) at 0.5 °C.min−1. During each trial participants provided ratings of TC at 3-min intervals to determine their thermal comfort zone (TCZ).
In the FAST trial, participants identified TCZ at an Ta between 22 ± 4 and 30 ± 4 °C during heating and between 25 ± 3 and 33 ± 3 °C during cooling phase (p = .003), and in the SLOW trial between 21 ± 3 and 33 ± 4 °C during heating and between 23 ± 4 and 34 ± 3 °C during cooling phase (p = .012). During the heating phase TCZ was established at a lower range of Ta, compared to cooling phase. The difference between the heating and cooling phases in preferred range of Ta was more pronounced in the FAST compared to SLOW trial.
TCZ is influenced not only by the prevailing temperature, but also by the direction and the rate of the change in Ta. Faster changes in Ta (1 °C.min−1) established the TCZ at a higher Ta during cooling and at a lower Ta during heating phase.
•Thermal comfort is influenced by the direction and the rate of change in the ambient temperature.•Heating established thermal comfort zone at lower ambient temperatures, compared to cooling.•Differences in the thermal comfort zones between the heating and cooling were more prominent at faster temperature changes.
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