Analysis of changes in cardiac circadian rhythms of RR and QT induced by a 60-day head-down bed rest with and without nutritional countermeasure

PURPOSE

Prolonged weightlessness exposure generates cardiovascular deconditioning, with potential implications on ECG circadian rhythms. Head-down (- 6°) tilt (HDT) bed rest is a ground-based analogue model for simulating the effects of reduced motor activity and fluids redistribution occurring during spaceflight. Our aim was to evaluate the impact of 60-day HDT on the circadianity of RR and ventricular repolarization (QTend) intervals extracted from 24-h Holter ECG recordings, scheduled 9 days before HDT (BDC-9), the 5th (HDT5), 21st (HDT21) and 58th (HDT58) day of HDT, the 1st (R + 0) and 8th (R + 7) day after HDT. Also, the effectiveness of a nutritional countermeasure (CM) in mitigating the HDT-related changes was tested.

METHODS

RR and QTend circadian rhythms were evaluated by Cosinor analysis, resulting in maximum and minimum values, MESOR (a rhythm-adjusted mean), oscillation amplitude (OA, half variation within a night-day cycle), and acrophase (φ, the time at which the fitting sinusoid's amplitude is maximal) values.

RESULTS

RR and QTend MESOR increased at HDT5, and the OA was reduced along the HDT period, mainly due to the increase of the minima. At R + 0, QTend OA increased, particularly in the control group. The φ slightly anticipated during HDT and was delayed at R + 0.

CONCLUSION

60-Day HDT affects the characteristics of cardiac circadian rhythm by altering the physiological daily cycle of RR and QTend intervals. Scheduled day-night cycle and feeding time were maintained during the experiment, thus inferring the role of changes in the gravitational stimulus to determine these variations. The applied nutritional countermeasure did not show effectiveness in preventing such changes.

P586Left ventricular volume and mass adaptation after 58-days head-down bed-rest assessed by cine-MRI, and effectiveness of high-intensity jump training countermeasure

Aims

Prolonged immobilization generates cardiac deconditioning, a risk factor for cardiovascular disease, and efficient countermeasures (CM) are needed to prevent it. Our aim was to assess by Cine-MRI the effects of long-term strict head-down (−6 degrees) bed-rest (BR) deconditioning, and the effectiveness of high-intensity jump training CM, on left ventricular (LV) function and mass.

Methods

23 male participants (29±6 years, 181±6 cm, 77±7 kg) were enrolled. The experiment was conducted at: envihab (Koln, DLR, Germany) as part of the European Space Agency BR studies. Volunteers were randomly allocated to the jump training group (JUMP, n=12) or the control group (CTRL, n=11). A typical training session consisted of 4x10 countermovement jumps and 2x10 hops in a sledge jump system, with 5–6 sessions per week.

Steady-state free precession cine-MRI images were obtained (25 frames/cardiac cycle, 8mm thickness, no gap, no overlap) as stack of short-axis images covering the whole LV from base to apex, before (PRE) and after 58-days (HDT58) of BR. Endocardial and epicardial semi-automated contouring was performed using custom software.

Results

In CTRL group, at HDT58 a reduction in LV mass (9%), end-diastolic (21%), end-systolic (8%) and stroke volume (23%) were observed, while ejection fraction did not change. In JUMP group, the reduction in LV end-diastolic volume was only by 9%, followed by a decrease in end-systolic (10%) and stroke volume (10%), with a preservation of LV mass. In both groups, ejection fraction did not change.

Left ventricular changes after 58d BR EDV (ml) ESV (ml) SV (ml) EF (%) Mass (g) CTRL PRE 171 (163; 191) 60 (58; 65) 113 (102; 124) 64 (63; 67) 133 (121; 160) HDT58 143 (131; 149)* 56 (50; 58)* 86 (83; 92)* 62 (60; 63)* 127 (106; 138)* JUMP PRE 156 (140; 204) 70 (61; 84) 91 (78; 117) 58 (56; 60) 118 (104; 134) HDT58 141 (135; 175)* 63 (54; 69)* 90 (78; 92)* 58 (55; 60) 113 (105; 128) Results expressed as median (25th; 75th percentiles). *p<0.05 Wilcoxon non parametric paired test (PRE vs HDT58). CTRL: control group; JUMP: countermeasure group.

Conclusions

Cardiac adaptation to deconditioning due to immobilization induced by BR resulted in a reduction of cardiac volumes and function, together with a decrease in LV mass. Interestingly, the applied JUMP countermeasure appeared able to partially reverse these effects, in particular by reducing the decrease in end-diastolic volume and preserving LV mass. This information could be useful for better understanding physiologic changes in patients undergoing long periods of immobilization, as well as to apply the studied countermeasure during space flight to reduce cardiac deconditioning.

Acknowledgement/Funding

Italian Space Agency (contract 2018-7-U.0),CNES/DAR 48ehz747.01950965,BELSPO, via the European Space Agency PRODEX program (PEA 4000110826)

[Dynamics of ECG voltage in changing gravity]

Comparative analysis of the QRS voltage response to gravity variations was made using the data about 26 normal human subjects collected in parabolic flights (CNERS-AIRBUS A300 Zero-G, n=23; IL-76MD, n=3) and during the tilt test (head-up tilt at 70 degrees for a min and head-down tilt at-15 degrees for 5 min, n=14). Both the parabolic flights and provocative tilt tests affected R-amplitude in the Z lead. During the hypergravity episodes it was observed in 95% of cases with the mean gain of 16% and maximal--56%. On transition to the horizontal position, the Rz-amplitude showed a rise in each subject (16% on the average). In microgravity, the Rz-amplitude reduced in 95% of the observations. The voltage decline averaged 18% and reached 49% at the maximum. The head-down tilt was conducive to Rz reduction in 78% of observations averaging 2%. Analysis of the ECG records under changing gravity when blood redistribution developed within few seconds not enough for serious metabolic shifts still revealed QRS deviations associated exclusively with the physical factors, i.e., alteration in tissue conduction and distance to electrodes. Our findings can stand in good stead in evaluation of the dynamics of predictive ECG parameters during long-term experiments leading to changes as in tissue conduction, so metabolism.

Quantification of left ventricular modification in weightlessness conditions from the spatio-temporal analysis of 2D echocardiographic images

Two-dimensional echocardiography (2DE) performed during flights with a parabolic trajectory to simulate weightlessness provides a unique means to study left ventricular (LV) modifications to prevent post-flight orthostatic intolerance in astronauts. However, conventional analysis of 2DE is based on manual tracings and depends on experience. Accordingly, the aim was objectively to quantify, from 2DE images, the LV modifications related to different gravity levels, by applying a semi-automated level-set border detection technique. The algorithm validation was performed by the comparison of manual tracing results, obtained by two independent observers with 20 images, with the semi-automated measurements. To quantify LV modifications, three consecutive cardiac cycles were analysed for each gravity phase (1 Gz, 1.8 Gz, 0 Gz). The level-set procedure was applied frame-by-frame to detect the LV endocardial contours and obtain LV area against time curves, from which end-diastolic (EDA) and end-systolic (ESA) areas were computed and averaged to compensate for respiratory variations. Linear regression (y = 0.91x + 1.47, r = 0.99, SEE:0.80cm2) and Bland-Altman analysis (bias = -0.58 cm2, 95% limits of agreement= +/- 2.14cm2) showed excellent correlation between the semi-automatic and manually traced values. Inter-observer variability was 5.4%, and the inter-technique variability was 4.1%. Modifications in LV dimensions during the parabola were found: compared with 1 Gz values, EDA and ESA were significantly reduced at 1.8 Gz by 8.8 +/- 5.5% and 12.1 +/- 10.1%, respectively, whereas, during 0 Gz, EDA and ESA increased by 13.3 +/- 7.3% and 11.6 +/- 5.1%, respectively, owing to abrupt changes in venous return. The proposed method resulted in fast and reliable estimations of LV dimensions, whose changes caused by different gravity conditions were objectively quantified.

ECG voltage modifications as response to gravity changes

The aim of the study was to analyze ECG (QRS) voltage responses to body fluid shift due to gravity chances. Acute changes in gravity were created by two ways: 1) changes in gravity value during parabolic flights (within 27 subjects 45 ECG have been analyzed); 2) changes in gravity direction due to rotation of the body during postural tests (within 11 subjects 14 ECG have been analyzed). Results and conclusions. Gravity change leads to body fluid shift and changes of intrathoracic organs and tissues electroconduction. It influences on ECG voltage. During parabolic flights in up-right position: R amplitude in Z axis increases in hypergravity (+0.19 mV) and decreases in microgravity (-0.24 mV). During postural tests, R amplitude in Z axis increases in orthostatic position (+0.09 mV) and decreases in antiorthostatic position (-0.025 mV). Changes in QRS voltage during parabolic flights are more important than during postural tests. This could be due to more effective blood redistribution during parabolic flights.

Feasibility of real-time 3D echocardiography in weightlessness during parabolic flight

Aim of the study was to test the feasibility of transthoracic real-time 3D (Philips) echocardiography (RT3D) during parabolic flight, to allow direct measurement of heart chambers volumes modifications during the parabola. One RT3D dataset corresponding to one cardiac cycle was acquired at each gravity phase (1 Gz, 1.8 Gz, 0 Gz, 1.8 Gz) during breath-hold in 8 unmedicated normal subjects (41 +/- 8 years old) in standing upright position. Preliminary results, obtained by semi-automatically tracing left ventricular (LV) and left atrial (LA) endocardial contours in multiple views (Tomtec), showed a significant (p<0.05) reduction, compared to 1 Gz, of LV and LA volumes with 1.8 Gz, and a significant increase with 0 Gz. Further analysis will focus on the right heart.

Changes in Doppler mitral inflow patterns during parabolic flight

Aim of the study was to evaluate by transthoracic Doppler the alterations in mitral inflow velocity pattern caused by acute changes in loading conditions occurring during parabolic flights. Each parabola included normogravity (1 Gz, 1 min), mild hypergravity (1.8 Gz, 20 sec), microgravity (0 Gz, 24 sec) and mild hypergravity (1.8 Gz, 20 sec) phases. Pulsed-Doppler images were digitally acquired in 11 unmedicated subjects (46 +/- 5 years), in standing upright position and supine resting. Doppler profiles were semi-automatically traced and inflow parameters extracted and averaged onto three consecutive beats. Only in standing position, significant alterations during microgravity (p<0.05) were noted in several parameters.

Changes of decartograms under gravitational acceleration and microgravity

The Decarto technique was used to study the orthogonal ECGs recorded in 23 subjects during parabolic flights (44 records). A parameter of the instantaneous decartograms, namely the activation area (AA), which is the total area of the depolarization front projection on the image sphere, was analyzed. We compared the values of AA during the periods of horizontal flight, upward parts of all parabolas, and the initial 10 s of microgravity of all parabolas. According to the characteristics of the vectorcardiograms and AA, all subjects were subdivided into 3 groups: with increased electric activity of the right ventricle (I), the left ventricle (II) and both ventricles (III). Changes of AA with change of gravitational levels in these groups showed some differences. In groups I and II, the AA of the initial part of the QRS complex increased during microgravity and decreased during hypergravity. In group III it decreased during microgravity and changed variously during hypergravity. The AA of the middle part of the QRS complex decreased during microgravity and increased during hypergravity, and these changes were more pronounced in group III. The changes of AA in groups I and II may be explained by the Brody effect. In group III, AA seems to be influenced by some additional factors, possibly by changes in the intramyocardial or intraventricular blood volume. The AA of the last part of the QRS complex increased during microgravity and decreased during hypergravity in all groups. This may be explained by an effect of mutual neutralization of depolarization fronts related to the changes of the QRS duration.(Fig. 3, Ref. 4)

Time-variant spectral analysis of heart rate variability during parabolic flight with and without LBNP

Modifications of autonomic activity during parabolic flight were studied by a time-variant model able to estimate low (LF, 0.04-0.14 Hz) and high (HF, 0.14-0.35 Hz) frequency spectral components on a beat-to-beat basis. Ten subjects were studied with and without lower body negative pressure (LBNP). ECG and Gz load were digitized (500 Hz) and RR interval variability series extracted. Beat-to-beat mean RR, variance, LF and HF power were obtained. One-way ANOVA (p<0.01) was used to compare values obtained during starting 1Gz (I), first 1.8Gz (II), 0Gz (III), second 1.8Gz (IV), ending 1Gz (V). Without LBNP, total and LF power increased during 0Gz to 1.69 +/- 1.41 and 2.87 +/- 4.66 respectively (mean +/- SD, normalized by phase I value). With LBNP, their change during 0Gz (1.38 +/- 1.37 and 1.54 +/- l.04 respectively) reached significance only with phase II and phase V. Phase I HF power was higher than in the other phases, both without and with LBNP.

Changes in left ventricular size during parabolic flights by two-dimensional echocardiography and level set method

This study aims to evaluate changes on cardiac chambers size, induced by gravitational stresses. During parabolic flight, seven subjects underwent 2-D transthoracic echocardiography at three different gravity phases (1 Gz, 1.8 Gz, and 0 Gz). LV endocardial borders were detected applying a semi-automatic segmentation procedure based on level set methods. LV cavity area was computed frame-by-frame for a whole cardiac cycle during each gravity phase. Expected modifications in LV area with different gravity were found: at 1.8 Gz, end-diastolic (ED) and end-systolic (ES) areas were significantly (p<0.05) reduced of 10.7 +/- 5.4% and 21.6 +/- 11.1% respectively, compared to 1 Gz values, while they were increased of 11.2 +/- 5.4% and 11.1 +/- 6% during 0 Gz. Fractional area change was augmented of 20.9 +/- 29.1% at 1.8 Gz, while it remained unchanged at 0 Gz, compared with 1 Gz values. Furthermore, LV filling due to atrial contraction was increased at 0 Gz of 39 +/- 35.6%.

Determination of lung capillary blood volume and membrane diffusing capacity in man by the measurements of NO and CO transfer

NO and CO lung transfer values (TL) were measured separately in 14 healthy subjects (7 men, 7 women), using the single breath technique. Five repetitive maneuvers were performed by each subject for TLNO and TLCO determinations. The inspired mixture contained either 8 ppm NO or 0.25% CO, with 2% He, 21% O2 in N2. In order to measure an appreciable fraction of NO in the alveolar gas it was necessary to shorten the breath holding time to 3 sec. TLNO was about five times greater than TLCO. This result suggests that the specific conductance of blood (theta) for NO is very high and that the second term of the second member of the equation 1/TLNO = 1/DmNO + 1/(theta NO.Qc) is therefore negligible. DmCO and Qc values can thus be computed from TLNO and TLCO measurements. The results obtained with this method are very close to those reported in the literature; for men DmCO = 79.0 +/- 14.3 ml.min-1.Torr-1, Qc = 78.0 +/- 13.2 ml and for women DmCO = 59.0 +/- 10.1 ml.min-1.Torr-1, Qc = 59.5 +/- 11.6 ml.

Prevention of exercise-induced asthma by oxitropium bromide

A vagal mechanism appears to be involved in the development of exercise-induced asthma (EIA), although previous studies have failed to demonstrate a protective effect of anticholinergic drugs against post-exercise bronchoconstriction. To reassess this hypothesis the effect of a new anticholinergic drug, Oxitropium Bromide (OTB) has been studied in ten subjects with documented EIA. There was no change after inhalation of a placebo. Administration of OTB led to bronchodilatation and totally blocked post-exercise bronchoconstriction in 7 patients, and it did so partly in 2. The response to the drug appeared to depend on pretest respiratory function. Thus, the anticholinergic drug OTB may protect against EIA in most patients, confirming the role of a vagal cholinergic mechanism in EIA.

BTPS calibration of heated Fleisch pneumotachometer

The Fleisch pneumotachometer (PTM) gives the instantaneous respiratory gas flow, and when integrated provides the volume of gas displaced. Its output signal is proportional to the product of the flow and the viscosity of the gas. The calibration factor is thus different for inspiration and expiration. Since the exact value of the viscosity is unknown, accurate figures for flow cannot be obtained. This study examines the use of a precisely sinusoidal pump with adjustable speed and capacity, displacing air in a thermostatically controlled chamber containing water at 37 degrees C stirred by a propellor. Thus air at ambient temperature flows through the PTM on inspiration, and on expiration the gas exactly simulates in temperature and humidity that normally expired by a human subject. This makes the output signal asymmetrical, with the expired volume VTE being greater than the inspired value, the ratio VTE/VTI = 1.035. Other sources of error, notably temperature and pressure changes in the chamber and differences in the proportions of O2 and CO2 in the expired gas, have been considered from both a theoretical and experimental standpoint. Their combined effects produce a less than 0.5% error. Using this pump, the Fleisch PTM can be calibrated empirically without making any assumptions about the temperature and viscosity of the expired gas mixture.

[Effect of a new synthetic anticholinergic (oxytropium bromide) on acetylcholine-induced bronchospasm]

Oxytropium bromide, a new synthetic anticholinergic agent, delivered by a dose inhaler, was compared to a placebo in a cross-over double-blind trial. The drop in FEV1 after administration of increasing doses of acetylcholine aerosol spray was measured 45 min after administration of the test drug, and the dose-response curve was determined. The placebo modified neither acetylcholine threshold dose (bronchial sensitivity) nor the slope of the curve (bronchial reactivity). Oxytropium bromide elevated the response threshold and decreased bronchial reactivity to vagal stimuli.

Mechanics and energetics of stilt walking

Three subjects were studied walking on a sports track with and without 1-m-long stilts. They were asked to walk in different ways. Pace length, step rate, heart rate, and oxygen consumption were measured under both conditions at different speeds. The results show that walking speed is generally faster for stilt walking than for normal walking. The higher speed is achieved due to increased pace length in spite of a decrease in step rate. The relationship between energy expenditure and walking speed is approximately the same in both cases. This result may be explained by two opposing factors: increase of pace length and decrease of step rate decrease the energy requirements of stilt walking, but the foot loading presented by the stilt walking exaggerates these conditions and increases energy expenditure.

[Respiratory function at rest in obese children (author's transl)]

Abnormalities of the respiratory function are a common finding in adult obesity. In order to investigate the occurrence of similar facts in pediatric age, a group of 39 obese children (20 girls and 19 boys, aged from 7 to 15 years) whose weight excess for their height ranged from 25 to 105 p. 100 was studied and compared to a control group of normal children of similar ages. Lung volumes, blood gases, transfer factor of the lung for CO, dynamic lung compliance, total lung resistance and ventilatory response to CO2 have been studied. In these obese children by contrast to obese adults, the vital capacity and the residual volume were normal. The blood gases, the transfer factor for CO, the dynamic lung compliance and the total resistances of the lung were similar to those of the normal group. The respiratory patterns were normal in all children but one who had during a short time a periodic ventilation with short periods of breath-holding. The ventilatory response to CO2 of the obese children was decreased and a highly significant correlation was found between the individual values of the respiratory response to CO2 and the percentage of weight excess. Different hypotheses are discussed to explain these results.

[Urogenital tuberculosis in antituberculosis dispensary practice]

The investigations carried out within the district depending upon the dispensary showed that urogenital tuberculosis incidence is in the second place, after respiratory tuberculosis; in 47% of the cases it was the only manifestation of the disease, in the other cases it was secondary to or accompanied other tuberculous localizations.