Work performance breathing normoxic nitrogen or helium gas mixtures

Summary Twelve subjects completed a progressive treadmill test to maximal aerobic capacity while breathing air or a 79% helium — 21% oxygen gas mixture (HeO₂). Metabolic and thermoregulatory responses to work while breathing the two mixtures were compared at rest, 30–40%, 60–70%, and 85–95% of maximal performance, and at maximal effort. Ventilation, ventilatory equivalent, and respiratory rates were increased and oxygen uptakes decreased by breathing HeO₂ when the level of work exceeded 85–95% of maximum. Heat loss through the respiratory tract was greater breathing HeO₂. The reduction in maximal oxygen uptake is probably due to a reduction in the oxygen cost of breathing a less dense gas. It was not related to a lower body temperature and probably not to O₂ transport or circulatory limitation. HeO₂ breathing had no effect on maximal mechanical work capacity.The nature and purpose of the study and the risks involved were explained verbally and given on a written form to each subject prior to his or her voluntary consent to participate. The protocol and procedures for this study have been approved by the Committee on Activities Involving Human Subjects, of the University of California, Santa Barbara, California, USA     

Psychophysiological Predictors of Attentional Dysfunction in Children with Congenital Heart Defects

Cardiac responses to non-signal stimuli and to signal stimuli in a vigilance task were examined in children born with congenital heart defects (CHD), and in normal and attention deficit disordered (ADD) subjects. Overall task performance was lower in subjects with heart defects and in the ADD group. Cardiac measures revealed that normal children displayed significantly larger heart rate deceleration to the target stimuli than did either of the clinical groups. Moreover, although no group differences were observed in the cardiac response to non-signal auditory stimuli, exaggerated heart rate deceleration was observed to vibrotactile stimuli in both the clinical groups. Regression analyses revealed that the magnitude of the cardiac response to somatosensory stimuli was predictive of task performance (both within and between subject groups), with larger responses associated with higher error rates and lower perceptual sensitivity. Results were suggestive of a predictive relationship between somatosensory reactivity and neuropsychological maturation.     

酮替酚对鸡蛋过敏特应性皮炎患儿淋巴细胞增殖反应的抑制作用

作者探讨了鸡蛋过敏特应性皮炎(AD)患儿外周血单个核细胞(PBMCs)对卵白蛋白(OA)刺激的增殖反应并观察了酮替酚(KF)对此反应的影响.结果提示AD患儿的PBMCs增殖反应显著高于健康儿童;KF可剂量依赖性地抑制鸡蛋过敏AD患儿PBMCs对OA刺激的增殖反应,且这一效应可通过KF抑制T细胞的作用而得以实现.KF对植物血凝素(PHA)和破伤风类毒素(TT)诱导的PBMCs增殖反应无抑制作用.这说明KF只抑制食物过敏AD患者PBMCs对食物抗原的特异性增殖反应.     

Electrodermal Orienting Responses to Onset and Offset of Auditory Stimulation under Nonsignal Conditions

It has previously been reported that the orienting reflex (OR) to the onset of a stimulus habituates more slowly than the OR to stimulus offset. In this paper, we attempted to account for this in terms of differences between the ON condition (whose presentation elicits the onset OR) and the OFF condition (whose “presentation” elicits the offset OR). Because the typical habituation paradigm begins with a period of adaptation to the OFF (stimulus absent) condition, the relative novelty of the ON condition is enhanced. This bias would contribute to the advantage of onset ORs over offset responses. This hypothesis was evaluated by comparing skin conductance responses (SCRs) to onset and offset of a 600 Hz tone in a group adapted in the presence of that tone (Tone Adaptation, TA) vs one adapted in its absence (Silent Adaptation, SA). The results supported our hypothesis; onset ORs habituated significantly more slowly than offset ORs in Group SA, but not in Group TA.     

Loads applied tangential to a fingertip during an object restraint task can trigger short-latency as well as long-latency EMG responses in hand muscles

Electrical stimulation of the digital nerves can cause short- and long-latency increases in electromyographic activity (EMG) of the hand muscles, but mechanical stimulation of primarily tactile afferents in the digits generally evokes only a long-latency increase in EMG. To examine whether such stimuli can elicit short-latency reflex responses, we recorded EMG over the first dorsal interosseous muscle when subjects (n=13) used the tip of the right index finger to restrain a horizontally oriented plate from moving when very brisk tangential forces were applied in the distal direction. The plate was subjected to ramp-and-hold pulling loads at two intensities (a 1-N load applied at 32 N/s or a 2-N load applied at 64 N/s) at times unpredictable to the subjects (mean interval 2 s; trial duration 500 ms). The contact surface of the manipulandum was covered with rayon—a slippery material. For each load, EMG was averaged for 128 consecutive trials with reference to the ramp onset. In all subjects, an automatic increase in grip force was triggered by the loads applied at 32 N/s; the mean onset latency of the EMG response was 59.8±0.9 (mean ± SE) ms. In seven subjects (54%) this long-latency response was preceded by a weak short-latency excitation at 34.6±2.9 ms. With the loads applied at 64 N/s, the long-latency response occurred slightly earlier (58.9±1.7 ms) and, with one exception, all subjects generated a short-latency EMG response (34.9±1.3 ms). Despite the higher background grip force that subjects adopted during the stronger loads (4.9±0.3 N vs 2.5±0.2 N), the incidence of slips was higher—the manipulandum escaped from the grasp in 37±5% of trials with the 64 N/s ramps, but in only 18±4% with the 32-N/s ramps. The deformation of the fingertip caused by the tangential load, rather than incipient or overt slips, triggered the short-latency responses because such responses occurred even when the finger pad was fixed to the manipulandum with double-sided adhesive tape so that no slips occurred.     

Cortico-cortical mediation of short-latency (lemniscal) sensory input to the motor cortex in deeply pentobitone anaesthetized cats

In pentobarbitone-anaesthetized cats, responses were recorded as surface positive potentials in the motor cortex on forelimb and brachium conjunctivum stimulation. In such a preparation, the forelimb nerve responses are mediated via the spino-cervical tract and the dorsal column-lemniscal pathway. Lesions of the sensory cortex (sparing only the depth of the coronary sulcus) abolished or reduced short-latency peripheral responses, in the motor cortex, on both skin and muscle nerve stimulation to less than 10% of control, while brachium conjunctivum responses were unchanged. Lesions of the second somatosensory area alone reduced the motor cortex responses on peripheral nerve stimulation by 10–20%. When the sensory cortex were abolished before the spreading depression reached the recording point, as judged from the brachium conjunctivum response. The depth distribution of positive and negative field potentials, constituting the early componentsof a peripheral response in the motor cortex, closely resembled that of a cortico-cortical response evoked on stimulation in area 3. It differed from that of thalamo-cortical response evoked in brachium conjunctivum stimulation. These data suggest that most, if not all, sensory input through the dorsal column and spino-cervical tract to the motor cortex is mediatd via the sensory cortex.     

Skin Conductance Conditioning to Potentially Phobic Stimuli as a Function of Interstimulus Interval and Delay Versus Trace Paradigm

Because prepared learning has been defined in terms of response acquisition in spite of degraded input, it was expected that differences in resistance to extinction between skin conductance responses conditioned to potentially phobic and neutral stimuli would increase with increased interstimulus interval (ISI) and be larger with a trace than with a delay conditioning paradigm. Twelve groups with 10 subjects each were observed in a differential conditioning experiment manipulating ISI (2, 8, or 16 sec), paradigm (delay versus trace), and fear-relevance of the conditioned stimulus (potentially phobic versus neutral). The results showed highly reliable resistance to extinction of first-interval anticipatory responses to phobic stimuli, and no resistance to extinction of the corresponding responses to the neutral stimuli. This difference did not interact either with the ISI or the paradigm factor. Thus, although underscoring the reliability of the difference in conditioning to potentially phobic and neutral stimuli, the results did not support the specific hypothesis of conditioning to phobic stimuli as being less dependent on the ISI parameters than conditioning to neutral stimuli.     

Conditioned Diastolic Blood Pressure as a Function of Induced Masseter Muscle Tension

The purpose of this study was twofold: 1) to attempt to replicate a previous study in which subjects were trained to produce bi-directional changes in diastolic BP as great as 10% to 15% of baseline, and 2) to determine whether the same subjects could acquire such a BP response under conditions of induced muscle tension. A 2x3 design was used in which 24 subjects were randomly assigned to one of two training procedures (feedback vs no feedback), and one of three muscular tension conditions. Acquisition took place over 14 sessions; 7 were used to train UP and 7 were used to condition DOWN responses. Results showed that during UP training, subjects learned to raise their BP in the absence of induced tension, but not when tension was present. However, the same subjects learned to lower their BP with and without induced tension, although their performance under the tension condition was only marginally reliable.     

ONSET AND TERMINAL ORIENTING RESPONSES AS A FUNCTION OF TASK DEMANDS

The frequency of response and trials to habituation of the electrodermal onset and terminal orienting response were manipulated as a function of discrimination tasks involving either stimulus content (pitch) or duration. There were no significant differences between the groups on either measure for onset ORs; however, the duration task group demonstrated more TORs and required a greater number of trials to habituate than the content task group. The results, interpreted in terms of the development of cortical models, supported Stern's suggestion that OR and TOR habituation are related to the content and duration of the stimulus respectively.     

Effects of Stimulus Intensity on Cardiovascular Activity

A between-groups design (N = 75) was employed to investigate the effects of stimulus intensity and repetition on cardiovascular activity. It was predicted that as intensity increased, the pattern of physiological activity would change, indicating a transition from the orienting to the defense reflex. Cardiovascular activity was represented by measures of heart rate, digital pulse amplitude, and cephalic blood content. Subjects received 12 presentations of a 1000 Hz tone of 45, 60, 75, 90, or 105 dB. Stimulus risetime was 30 msec and the duration 2 sec. Analyses of variance revealed reliable effects of intensity and repetition on all cardiovascular variables. However, neither these results nor additional multivariate analyses supported the differentiation of orienting and defense reflexes as suggested by Sokolov (1963) or Graham (1979). The importance of the startle reflex in the interpretation of these findings was discussed.