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Biomedical subjects

J W Fitting

Publications and source records attributed to J W Fitting.

At least 55 records · Page 3Linked to original sources
PubMed1994

Regulation of inspiratory neuromuscular output during synchronized intermittent mechanical ventilation.

BACKGROUND: In synchronized intermittent mandatory ventilation, it is generally accepted that the work of the inspiratory muscles is decreased by the ventilator so that their activity can be modulated by the frequency of assisted breaths. We examined the validity of this concept, which recently has been questioned. METHODS: We studied five patients receiving synchronized intermittent mandatory ventilation because of an acute exacerbation of chronic obstructive pulmonary disease. The level of machine assistance, defined as the percentage of total ventilation delivered by the ventilator, was varied from a high (> 60%) to a medium (20-50%) and to the lowest tolerated value (0% in four patients). Esophageal pressure, air flow, and the electromyograms of the diaphragm and sternocleidomastoid muscles were recorded. At each level of machine assistance, distinguishing assisted from spontaneous breaths, the duration of electrical activation, the integrated electromyograms, and the work of breathing were computed. RESULTS: The durations of electrical activation and the integrated electromyograms of the diaphragm and sternocleidomastoid were similar in successive spontaneous and assisted breaths. At > 60% of machine assistance, the cumulative values per minute of the integrated electromyograms of the diaphragm and sternocleidomastoid and the work of breathing were reduced only by 38, 32, and 44%, respectively, compared with the lowest tolerated level of machine assistance. The durations of electrical activation did not change with increasing level of machine assistance. CONCLUSIONS: The degree of inspiratory muscle rest achieved by synchronized intermittent mandatory ventilation is not proportional to the level of machine assistance; furthermore, the inspiratory motor output is not regulated breath by breath but rather is constant for a given level of machine assistance.

Aged↗
PubMed1994

Sniff nasal inspiratory pressure. A noninvasive assessment of inspiratory muscle strength.

The measurement of esophageal pressure during maximal sniffs (sniff Pes) has been shown useful to assess inspiratory muscle strength. The aim of this study was to validate a noninvasive method for estimating sniff Pes. The sniff nasal inspiratory pressure (SNIP) was measured through a plug occluding one nostril during sniffs performed through the contralateral nostril. Sniff Pes was simultaneously measured with an esophageal balloon. Ten normal subjects performed 338 sniffs of variable intensity. The correlation coefficient of SNIP and sniff Pes was 0.99 +/- 0.01 (p < 0.001). The ratio SNIP/sniff Pes was 0.91 (range, 0.82 to 0.99) and the mean difference between the two measures (SNIP - sniff Pes) was -4.56 cm H2O (-1.2 to -8.6 cm H2O). Twelve patients with neuromuscular or skeletal disorders performed 181 maximal sniffs. The correlation coefficient of SNIP and sniff Pes was 0.96 +/- 0.04 (p < 0.001). The ratio SNIP/sniff Pes was 0.93 (0.77 to 1.07) and the mean difference (SNIP - sniff Pes) was -4.66 cm H2O (+0.47 to -14.26 cm H2O). Nasal mucosal congestion was induced by nebulization of increasing doses of histamine in four normal subjects. The ratio SNIP/sniff Pes was 0.93 (0.72 to 1.02) when nasal peak flow was > 100 L/min, and 0.49 (0.36 to 0.57 L/min) when nasal peak flow fell below 100 L/min. We conclude that SNIP provides a reliable and noninvasive estimation of sniff Pes in normal subjects and in patients with neuromuscular or skeletal disorders. The validity of this method may by impaired by severe nasal congestion.

Adult↗
PubMed1994

Respiratory muscles during ventilatory support.

Knowledge of the fate and behaviour of the respiratory muscles during ventilatory support is important for the guidance of clinical care. Full support facilitates muscle metabolic repletion, but exposes them to the risk of disuse atrophy. The effect of partial support varies according to the selected mode: assisted mechanical ventilation (AMV) and synchronized intermittent mechanical ventilation (SIMV) result in much less respiratory muscle rest than generally anticipated. On the other hand, inspiratory pressure support (IPS) is able to rest the respiratory muscles and to prevent fatiguing contractions. Opposite interventions have been proposed in case of difficult weaning: either to unload the respiratory muscles by using partial support, or to overload them according to a training programme. The optimal strategy is not known and may combine both approaches.

Humans↗
PubMed1993

[Mechanical ventilation at home: facts and questions].

Treatment of respiratory insufficiency with retention of CO2 by mechanic ventilation has come into use over the last decade, favored by use of non-invasive methods like nasal ventilation. Best results have been observed in hypercapnic respiratory insufficiency caused by neuromuscular disease or restrictive pathologic changes of the lung. Nocturnal use of nasal ventilation alone is often sufficient to correct also the daily CO2-values. Mechanisms explaining this beneficial effect are not yet known-The respiratory CNS-centers, respiratory muscles or thoracopulmonary mechanics may play etiologically an important role. Medical indications for nasal ventilation in chronic obstructive pulmonary disease are not clear, since results from several studies are controversial. Also in severe or progressive neurologic diseases a critical evaluation is mandatory for assessment of benefits including improvement of quality of life.

Carbon Dioxide↗
PubMed1993

Costal and crural diaphragm function during CO2 rebreathing in awake dogs.

If costal and crural diaphragm segments can perform as separate muscles, then CO2-stimulated ventilation may elicit differential segmental function. We studied diaphragm segmental length, shortening, and electromyogram (EMG) activity in 10 awake dogs chronically implanted with sonomicrometer transducers and EMG electrodes. During CO2 rebreathing, segmental shortening and EMG activity per whole tidal breath progressively increased, but segmental responses could not be differentiated at any level of CO2. With increasing CO2, resting end-expiratory length of both diaphragm segments increased. During the complete intrabreath inspiratory-expiratory cycle, costal and crural diaphragm revealed distinctive segmental function. At rest, crural shortening exceeded costal shortening in earliest inspiration, costal and especially crural shortening persisted into early expiration, and EMG activity of the crural segment was greater than that of the costal segment in earliest inspiration and showed more end-inspiratory/early expiratory [post-inspiratory inspiratory activity (PIIA)] activity. During CO2-stimulated breathing, neither segment shortened during the inspiratory flow of earliest inspiration. During CO2 rebreathing, shortening of the crural segment exceeded that of the costal segment during early inspiration and outlasted costal shortening during expiration; for both segments, shortening persisted after termination of inspiratory airflow. With increased CO2, EMG activity of the crural segment preceded that of the costal segment in earliest inspiration and was dominant into expiration, whereas costal EMG activity terminated abruptly with inspiratory flow. Thus, costal EMG PIIA was not evident during hypercapnia, whereas crural EMG PIIA was significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Effect of pressure and timing of contraction on human rib cage muscle fatigue.

Breathing against inspiratory loads can be accomplished with different degrees of coupling between the diaphragm and the other muscles attached to the rib cage (RCM). Thus, the electromyographic signs of fatigue develop separately in each muscle group. While breathing with diaphragm emphasis, the occurrence of diaphragmatic fatigue was found to be related to the tension-time index TTdi (= Pdi/Pdimax x Ti/Ttot). Above the critical range of 0.15 to 0.18, the endurance of the diaphragm is less than 1 h and it is inversely related to the TTdi value. However, in most loaded breathing conditions, the spontaneous pattern of breathing is characterized by predominant activation of RCM. The tension-time conditions at which fatigue develops during breathing with RCM emphasis are not known. We assessed the critical tension-time value in four normal subjects breathing with RCM emphasis against inspiratory threshold loads. RCM predominance was achieved by developing negative abdominal pressure swings during inspiration, and it was characterized by the tension-time index TTrc (Ppl/Pplmax x Tl/Ttot), where Ppl is pleural pressure developed under this condition. Above a critical TTrc value of 0.30, endurance time was inversely related to TTrc, and it resulted from failure of the RCM rather than of the diaphragm. We conclude that the critical threshold, as assessed by TTrc, is higher for breathing patterns with RCM emphasis than previously described by TTdi for diaphragm emphasis. However, when predominantly recruited, as in breathing patterns commonly adopted in loaded conditions, the RCM fatigue earlier than the diaphragm.

Adult↗
PubMed1993

Diet-induced thermogenesis in chronic obstructive pulmonary disease.

Increased resting energy expenditure and malnutrition are frequently observed in patients with COPD. The aim of this study was to examine the possible contribution of an increased diet-induced thermogenesis (DIT) to weight loss. Eleven patients with COPD in stable clinical state and 11 healthy control subjects were studied. Resting energy expenditure (REE) was measured by standard methods of indirect calorimetry, using a ventilated canopy. Premeal REE was measured after an overnight fast. All subjects then received a balanced liquid test meal with a caloric content that was 0.3 times their REE extrapolated to 24 h. Diet-induced thermogenesis was measured over 130 min. Premeal REE was 109.9 +/- 11.7% of predicted values in the COPD group and 97.5 +/- 9.6% of predicted in the control group (p < 0.01). Seventy minutes after the test meal, REE had increased by 18.8 +/- 8.5% in the COPD group and by 15.1 +/- 5.8% in the control group (NS). After 130 min, REE had increased by 16.4 +/- 7.1% in the COPD group and by 12.4 +/- 5.3% in the control group (NS). The DIT expressed as a percentage of the caloric content of the meal was 4.3 +/- 1.6% in the COPD group and 3.3 +/- 1.4% in the control group (NS). We conclude that patients with stable COPD, although hypermetabolic at rest, do not show an increased DIT.

Basal Metabolism↗
PubMed1993

[The pulmonary manifestations of diving accidents].

Scuba diving is associated with risks of drowning, lung barotrauma and decompression sickness. In case of near-drowning, irreversible neurologic lesions or death may follow an acute hypoxemia or a cardiopulmonary arrest. Therefore, victims of drowning should benefit from an immediate and prolonged cardiopulmonary resuscitation. Lung barotrauma are due to the failure of expanding lung gases to escape during ascent; they are likely to be complicated by arterial gas embolism. They can follow a panic ascent even from a shallow depth. Most of decompression procedures induce the formation of asymptomatic venous gas bubbles, normally filtrated and eliminated by the lungs. In case of massive intravenous bubbling, the filtering capacity of the lungs can be overwhelmed and the lung microcirculation damaged up to the point of provoking a cardio-respiratory failure.

Adult↗
PubMed1992

[Respiratory rehabilitation].

Pulmonary rehabilitation is directed at all patients with severe chronic respiratory insufficiency of any origin. Patients with chronic obstructive pulmonary disease clearly represent the majority. In a pulmonary rehabilitation programme, the patient must gain a better understanding of his disease and of the goals of the treatment. He benefits from permanent teaching on methods of independent self-treatment and follows a regular programme of exercise training and nutritional support aimed at increasing effort capacity. The ultimate goal of the programme is to send the patient home with improved quality of life and a higher degree of independence.

Breathing Exercises↗
PubMed1992

[Fatigue of the respiratory muscles].

Respiratory muscle fatigue is induced experimentally by adding high external resistances to breathing. The role played by respiratory muscle fatigue in exercise limitation and in acute respiratory failure is still unclear. The electromyogram often reflects contractions beyond the fatigue threshold, but overt force failure has been only rarely demonstrated under these circumstances. Hypercapnic ventilatory failure may possibly not result from fatigue, but rather from an adaptation of the respiratory system for avoiding fatigue. The treatment of fatigue comprises respiratory muscle support by adequate nutrition and oxygen delivery, and if needed respiratory muscle rest by mechanical ventilation.

Airway Resistance↗
PubMed1991

[Nutrition in chronic obstructive bronchopneumopathy].

The respiratory system and nutrition are linked. Obesity is sometimes seen in chronic obstructive pulmonary disease (COPD), but its prevalence, the morbidity and mortality induced by it are not known. In addition, the prevalence of malnutrition is high in COPD and the more severe the COPD is, the higher percentage of malnutrition is present. Emphysematous patients are more frequently undernourished than those suffering from chronic bronchitis. Malnutrition is the consequence of the hypermetabolism induced by the higher cost of breathing in emphysema. The survival rate of these patients is negatively affected by malnutrition. A careful assessment of nutritional status must be performed in all COPD patients, especially during an episode of acute respiratory failure. When signs of malnutrition are present, a nutritional intervention should be initiated rapidly. An amount of calories sufficient to meet the energy expenditure increased by the disease must be given. Excessive intake may overstress the respiratory system whose functional reserve is limited in COPD. The diet must include a well balanced percentage of fat, carbohydrates and proteins. Preservation of the fat-free mass is the minimum goal to reach in acute respiratory failure. After the resolution of the acute phase, a gain of weight should be attempted within a rehabilitation program.

Bronchitis↗
PubMed1991

[Home mechanical ventilation in Switzerland in 1990. Future developments].

Home mechanical ventilation (HMV) was initiated in polio centers in the mid-50s (iron lung). Ten years ago, chronic respiratory insufficiency patients began to be treated with positive pressure ventilation via tracheostomy tube. Survival of kyphoscoliotic and myopathic patients was impressive in uncontrolled studies. Today it appears that similar results may be obtained with a new non-invasive technique, nasal mechanical ventilation. The present situation of HMV in Switzerland (number of patients and their location) and the results of this treatment are described. In addition, we report on a short series of 24 Swiss patients collected in 4 centers. We show that HMV is possible in Switzerland and that the results in survival and quality of life are excellent, provided that the indications for this technique are consistent with the recommendations in the literature.

Adolescent↗