Sleep monitoring: the second manned Skylab mission.

The first objective measurements of man's ability to obtain adequate sleep during prolonged space flight were made during the three manned Skylab missions. EEG, EOG, and head-motion signals were acquired during sleep by use of an elastic recording cap containing sponge electrodes and an attached miniature preamplifier/accelerometer unit. A control-panel assembly, mounted in the sleep compartment, tested electrodes, preserved analog signals, and automatically analyzed data in real time (providing a telementered indication of sleep stage). One subject was studied during each manned mission and, while there was considerable variation among individuals, several characteristics were common to all three: stage 3 sleep increased during the flight and decreased in the postflight period; stage 4 was consistently decreased postflight, although this stage was variable during the flight; stage REM (rapid eye movement) was elevated, and REM latency decreased in the late postflight period (after day 3 postrecovery); and the number of awakenings during sleep either showed no change or decreased during the flight. In only the 28-d mission (Skylab 2) was there a significant decrease in total sleep time; in that case it was a result of voluntarily reduced rest time and was not due to difficulty in sleeping nor frequent awakening. The subject on the 84-d mission (Skylab 4) experienced more difficulty in the first half of the flight, showing a decreased total sleep time and increased sleep latency, but this resolved itself with time. Sleep latency presented no problem in the other flights. While many of the findings are statistically significant, in no case would they be expected to produce a noticeable decrement of performance capability. These findings suggest that men are able to obtain adequate sleep in regularly scheduled 8-h rest periods during extended space flights. It seems likely, based upon these results, that the problems encountered in earlier space flights did not arise from the zero-g environment per se but possibly were a result of more restricted living and working areas in the pre-Skylab spacecraft.     

Exercise cardiac output following Skylab missions: the second manned Skylab mission.

Cardiac output was measured during preflight and postflight exercise-stress tests on the Skylab astronauts. In the postflight tests immediately following the 28-, 59-, and 84-d earth orbital missions, the astronauts exhibited an approximate 30% decrease in cardiac output coupled with an approximate 50% decrease in cardiac stroke volume during exercise. These changes were accompanied by elevated heart rates and significant (p less than 0.01) increases in total systemic peripheral vascular resistance. Mean arterial pressure was unchanged. The hemodynamic alterations were transient in that all parameters returned to normal preflight values within 30 d of the end of the orbital period. Duration of the zero-G exposure did not appear to influence either the magnitude of the hemodynamic changes or the time-course of their return to normal. These results are discussed in relation to other cardiovascular findings and possible mechanisms responsible for the observations are outlined.     

Bone mineral changes: the second manned Skylab mission.

The mineral content of the central os calcis, and distal radius and ulna was measured by the monoenergetic photon absorptiometric technique pre- and postflight on the the SL-3 crewmen. No significant changes were observed in the radius and ulna. Only the SPT showed a loss in calcaneal mineral which slowly returned to preflight levels by the 87th postflight day.     

Metabolic and endocrine studies: the second manned Skylab mission.

This study conducted on the crewmembers of Skylab 3 was designed to evaluate the endocrinological adaption resulting from extend exposure to a space flight environment by identifying changes in hormonal and associated fluid and electrolyte parameters. The three men served as their own controls and were on a constant dietary intake. Complete metabolic collections were performed beginning 21 d before the flight, continuing throughout the flight, for 18 d postflight. Changes in fluid and electrolyte balance have been correlated with weight loss, changes in the excretion of aldosterone, vasopressin, and fluid compartments. Inter-individual variability was demonstrated in most experimental indices measured; however, statistically significant patterns have emerged which include: decreases in body weight and ADH, increases in plasma renin activity, and elevations in urinary catecholamines, aldosterone and cortisol concentrations. Urinary sodium was increased in flight but potassium was only slightly changed. Total body exchangeable K was slightly decreased in all three of the crewmen. Total body water and extracellular fluid were decreased postflight in almost all cases. The measured changes are consistent with the prediction that a relative increase in thoracic blood volume upon transiton to the zero gravity environment is interpretated as a true volume expasion resulting in a net fluid loss. This, in association with other factors, ultimately results in a reduction in intravascular volume leading to an increase in renin and a secondary aldosteronism. Once these compensatory mechanisms are effective in reestablishing positive water balance, the crewemn are considered to be essentially adapted to the space environment. Although the physiological cost of this adaptation must reflect the electrolyte deficit and perhaps other factors, it is assumed that the compensated state is adequate for the demands of the environment; however, this new homeostatic set is not believed to be without physiological cost and could, except with proper precautions, reduce the functional reserve of exposed individuals.     

Hematology and immunology studies: the second manned Skylab mission.

The hematologic and immunologic functions of the Skylab 3 (second manned mission) astronauts were examined during the preflight, inflight, and postflight phases of the 59-d mission in order to evaluate the response to and/or the influence of the space flight environment. Most changes observed were subtle and did not represent a threat to the health and safety of the crewmen during orbital flight. Even the most significant change observed, a reduction in the circulating red cell mass, did not have a detrimental influence on the astronaut cardiovascular or exercise responses as evaluated by other experiment protocols. Considering the facts that the data were not collected under ideally controlled conditions and that the astronauts were in excellent physical condition, the results of these studies would seem to indicate that man can function quite well in the space flight environment of the Skylab orbiting workshop for extended periods of time.     

Lower body negative pressure: the second manned Skylab mission.

Results of orthostatic evaluations of the crew of Skylab 3 with lower body negative pressure (LNBP) stress tests during their 59-d mission are reported. The test protocol was identical to that used in the first manned Skylab mission and the latter Apollo flights. Except for an inflight increase (rather than a decrease) in resting heart rates, results were essentially parallel to those observed in crewmen of the shorter Skylab 2 mission. Exaggerated elevations in heart rate and decreases in pulse pressure during LBNP stress inflight and immediately postflight corresponded to lowered orthostatic tolerance. Large decrements in resting calf size inflight and in total leg volume postflight indicated significant headward fluid shifts as had already been seen in the Skylab 2 crewmen. In addition, decreases in calf circumference gave no certain indication of a plateau over the 59 d inflight. On the other hand, percentage volume increase in calf size during LBNP stress inflight was greater than those in either preflight or postflight tests. Hypotheses elaborated after the Skylab 2 mission seem to have been substantiated, but several enigmas await data from the last and longer mission for clarification.     

Mineral and nitrogen balance study observations: the second manned Skylab mission.

A metabolic study of the effects of space flight on various chemical elements, particularly those with special revelance to the musculoskeletal system, was carried out on the three astronauts of the SL-3 mission for 21 d preflight, during the 60 d flight phase, and for 17 d postflight. The study required of the cooperating crewmen quite constant dietary intake, continuous 24-hour urine collections and total fecal collections. Urinary calcium was significantly increased during flight in all three crewmen with man-to-man variation in pattern and amount; the degree of calcium loss was, in general, similar to that in the prior study of the 28-d Skylab flight (SL-2). The similarity to bedrest immobilization in the pattern of urinary calcium increases and of total calcium shifts suggested that calcium losses would continue for a very long time. Significant losses of nitrogen and phosphorus occurred that were associated with observed reduction in muscle tissue. Both mineral and muscle losses occurred despite vigorous exercise regimens during flight. It was concluded that these studies give warning that capable musculoskeletal function may be significantly impaired during prolonged space flights lasting 1.5 to 3 years unless protective measures are developed.     

Crew health status and monitoring summary: the second manned Skylab mission.

We have attempted to show that objective data used to assess crew health comes to the responsible physicians from the laboratories of the experimenters in sporadic and overwhelming amounts, but rarely in the real-time or near real-time frame which is preferred. The crew surgeon generates little hard data by his own efforts. Because of these factors, whenever an over-all clinical assessment of a particular crewman's fitness to continue a mission is an immediate necessity, it must too often be given on what the clinician would consider less than adequate data. Beginning on MD 28, weekly conferences were held with senior NASA management to make a "Go" or "No-Go" recommendation to continue or terminate the mission. In the absence of absolute indications of an unacceptable declining crew health, a clinical judgment was required. To tighten the criteria for decision-making, the authors selected factors that seemed indicative of overall health and plotted them both as real-time and percentage changes from preflight means. Other plots of the most readily available real-time and near real-time data were also developed for this purpose. The major success of this effort was the initiation of a method which indicated interesting and worthwhile possibilities if continued, refined, and computerized for more rapid availability. Correlation of actual post-flight findings with results anticipated from this method was gratifying but not statistically defensible. Whether or not this method would have forewarned of a serious decrement in crewmen's health cannot be known because, in fact, they were healthy and remain healthy.     

Quantitative electrocardiography during extended space flight: the second manned Skylab mission.

To assess the effects of space flight on cardiac electrical properties, vectorcardiograms (VCG) were obtained on the Skylab crew at regular intervals during the 59-d flight (SL3) and during the pre- and postflight periods. The Frank lead system was used and observations were made at rest; during 25%, 50%, and 75% of maximum exercise; during a short pulse of exercise (150 W, 2 min); and after exercise. Data from 47 in-flight tests were analyzed by computer and compared to preflight and postflight values. A statistically significant increase in QRS maximum vector magnitude (all SL3 crewman); and an increase in resting PR interval (all SL3 crewmen) occurred. During exercise, the PR interval did not differ from preflight. Exercise heart rates in flight were same as preflight, but increased in the immediate postflight period. No major changes in QRS, T, or ST vector direction occurred. The scientist pilot had premature ventricular beats sporadically during the flight. This astronaut also had intermittent periods of atrioventricular junctional rhythm throughout the flight. The increase in QRS maximum vector magnitude resembles the electrocardiographic changes associated with athletic conditioning and may be related to increased ventricular volume secondary to centripetal shifts of fluid and/or the in-flight isotonic exercise program. Prolongation of the PR interval at rest with normalization of exercise suggests that there was increased vagal tone or suppressed sympathetic influence during the flight.     

Pre- and postflight systolic time intervals during LBNP: the second manned Skylab mission.

After space flight of 59 d, Skylab 3 astronauts were stressed with lower body negative pressure (LBNP). During this stress procedure vectorcardiograms, pneumograms, phonocardiograms, and carotid pulse tracings were monitored and recorded onto analog tape. Accepted techniques were used to measure the intervals of systole. The postflight results were compared to multiple preflight tests and each of the three crewmen served as his own control. Immediately postflight, there were elevations in heart rate and blood pressure in response to a fixed level (-50 mm Hg) of LBNP. Total electromechanical systole, (Q-S2) I, was unchanged. Ejection time index (ETI) was depressed at rest and during stress, while pre-ejection period was elevated compared with preflight values. Systolic time intervals (STI) were within preflight limits after 1 month on earth in all crewmen. Resting STI returned sooner than did stressed STI. The magnitude and direction of STI in the postflight period were similar to those obtained from patients with moderate heart disease, although signs and symptoms were absent in the astronauts. However, the abnormality of the stressed STI persisted after both blood volume repletion and lowered afterload. These findings suggest a compromise in cardiac function, peripheral circulatory integrity, or both after exposure to long-duration space flight, and are consistent with findings reported after 3 weeks of absolute bedrest.     

Determination of cardiac size following space missions of different durations: the second manned Skylab mission.

A simple method to estimate cardiac size from single frontal plane chest roentgenograms has been described. Pre- and postflight chest X-rays from Apollo 17, and Skylab 2 and 3 have been analyzed for changes in the cardiac silhouette size. The data obtained from the computed cardiothoracic areal ratios compared well with the clinical cardiothoracic diametral ratios (r = .86). Though an overall postflight decrease in cardiac size is evident, the mean difference was not statistically significant (n = 8). The individual decreases in the cardiac silhouette size postflight are thought to be due to decrements in intracardiac chamber volumes rather than in myocardial muscle mass.     

Measurement of compartment size in q-space experiments: Fourier transform of the second derivative.

Restricted diffusion in compartmentalized systems can lead to spatial coherence phenomena being observed in q-space plots from pulsed field gradient spin-echo (PGSE) nuclear magnetic resonance (NMR) experiments. The underlying features observed in these plots contain information on the geometry of the compartments that is otherwise difficult to obtain. A numerical procedure is proposed that accentuates these coherence features: the data are weighted with a bell-shaped window function, interpolated with a shifting cubic spline, and then the second derivative is taken prior to Fourier transformation. The window function provides apodization of the noisy data at high q values, while it and the second derivative are equivalent to applying a high-pass filter to remove the zero- or low-frequency components in the echo-signal attenuation. Using a combination of theory, Monte Carlo simulations, and data from PGSE NMR experiments on human red blood cells, we demonstrate this to be a valuable processing tool for delineating the underlying coherence features. It should prove particularly useful where the coherence features are poorly defined or where more than one pattern is present in a q-space plot.     

Reconstruction of the ACL with a semitendinosus tendon graft: a prospective randomized single blinded comparison of double-bundle versus single-bundle technique in male athletes

Anterior cruciate ligament (ACL) reconstruction in double-bundle technique is advocated to more closely restore the anatomy and function of the native ligament than conventional single-bundle technique. But up to now there are only a few clinical investigations comparing both techniques in a prospective manner. We hypothesized that double-bundle ACL reconstruction reveals superior clinical and subjective results compared to single-bundle technique in a high-demand collective. A total of 50 male patients (mean age 29.4 years) were prospectively randomized consecutively into one of the two reconstruction techniques. Group 1 (SB) underwent a 4-stranded single-bundle reconstruction with a ST graft in femoral position at 10:00 and 02:00 o’clock, respectively. In group 2 (DB), reconstruction was performed by using a 2-stranded ST graft with double-bundle, four tunnel technique. Before surgery and at a 2 year follow-up (range 23–25 months) patients were evaluated by the same blinded observer. There was no significant difference in the side-to-side anterior laxity-measurement with the KT-1000 between both groups. As evaluated by the pivot shift, no significant correlation could be noted (Fisher exact test P = 0.098) between rotational stability and any of the both reconstruction techniques. However, the anterior and rotational stability improved significantly at 2-year follow-up compared to preoperatively (P = 0.003) in both groups. The statistical analysis showed a significant increase for the IKDC (subjective, objective) and the Lysholm Score at final follow-up among each single technique, while we found no significant difference between the two reconstruction methods. On the basis of our investigation, we conclude that reconstruction of the ACL by a double-bundle ST graft with an extracortical anchorage can achieve excellent clinical results. But in contrast to our initial hypothesis, we could not quote any significant advantages by creating two independent bundles. Reconstruction of the anterior cruciate ligament in conventional single-bundle technique with a more horizontal femoral tunnel placement obtains comparable clinical results in the present high-demand collective.     

Measurement of tendon excursion velocity with colour Doppler imaging: a preliminary study on flexor pollicis longus muscle

Purpose: To study the use of colour Doppler imaging (CDI) for the measurement of maximum and mean tendon velocity. Recent studies showed that CDI, normally used for blood flow examinations, can be used for the imaging of tendons at the hand and wrist region. Although other modalities are available for imaging of the musculo-skeletal system, in vivo measurements of the velocity of tendon excursion are not possible. Methods: The flexor pollicis longus (FPL) tendon of 16 healthy volunteers was measured bilaterally at two levels (wrist and thenar). A splint from the fingers along the proximal lower arm was applied. The thumb was fixed to the splint from the first phalanx to allow flexion of the interphalangeal (IP) joint only. Pulsed CDI was used for the measurements. The maximum and mean velocities of the FPL tendon were measured at spectrum display mode during continuous voluntary contractions. At least 10 sequential Doppler peaks (cm/s) were recorded at every trial. The measurements were repeated three times. Paired t-test and correlation coefficients were calculated between levels on the same side and the opposite side. Results: No significant differences were found between two levels of the same hand and of the opposite hand. As expected, the data revealed variations in the inter-individual tendon velocities. Conclusions: The velocity of the excursion of the FPL tendon can be measured with CDI with good reproducibility. It is expected that velocity measurements can be used in the future for the assessment of other tendons affected by various disorders.     

Simultaneous anatomic reconstruction of the acromioclavicular and coracoclavicular ligaments using a single tendon graft

Purpose

The purpose of this study was to introduce a novel surgical technique for simultaneous anatomic reconstruction of the acromioclavicular and coracoclavicular ligaments using a single tendon graft and to compare its biomechanical characteristics to those of a coracoid cerclage reconstruction of the coracoclavicular ligaments.

Methods

Six matched pairs of human acromioclavicular joints with an average age of 54.8 ± 7.8 years were used. One shoulder from each pair received the single tendon acromioclavicular–coracoclavicular reconstruction; the contralateral shoulder received the coracoid cerclage reconstruction. Bovine extensor tendon was used for both techniques. The single tendon acromioclavicular–coracoclavicular reconstruction technique provided anatomic restoration of the two coracoclavicular ligaments and the superior and inferior acromioclavicular ligaments simultaneously using one coracoid hole, one acromion hole, and two clavicular holes with interference screws. Anterior–posterior and superior–inferior translations were quantified for all specimens before and after reconstruction, followed by load to failure testing.

Results

Following coracoid cerclage reconstruction, total anterior–posterior translation was significantly greater than intact (10.0 ± 5.7 mm; p = 0.008). Following single tendon acromioclavicular–coracoclavicular reconstruction, there was no significant difference in anterior–posterior translation compared to intact (?1.6 ± 2.2 mm; n.s.). The coracoid cerclage technique demonstrated significantly greater anterior–posterior translation than the single tendon acromioclavicular–coracoclavicular technique (p = 0.007). Both techniques restored superior–inferior translation to the intact condition (n.s.). Ultimate load, deformation at ultimate load, and energy absorbed at ultimate load were significantly greater after acromioclavicular–coracoclavicular reconstruction than after coracoid cerclage reconstruction (p < 0.05).

Conclusions

This novel single tendon anatomic acromioclavicular–coracoclavicular reconstruction provided greater stability and stronger load to failure characteristics than the isolated coracoid cerclage reconstruction. A simultaneous acromioclavicular–coracoclavicular reconstruction technique using a single free tendon graft provided anatomic reconstruction of the conoid, trapezoid, and superior and inferior acromioclavicular ligaments and may reduce postoperative subluxation.