Jan Weinberg

Polysomnography in Chronic Neuromuscular Disease

Background: Sleep is a risk factor for respiratory failure in patients with chronic neuromuscular diseases (NMD). Objective: To explore the diagnostic value of monitoring sleep parameters in addition to nocturnal respiratory parameters. Methods: Thirty-one patients with chronic NMD underwent whole-night polysomnograms including EMG from accessory respiratory muscles. Results: Sleep macrostructure was normal on average. The number of respiratory arousals per hour of sleep was above the upper limit observed in a control group (>2.1) in 71% of the patients, but was moderate in most cases. Nadir oxygen saturation <85% was the most common finding indicating respiratory dysfunction and was present in 80% of the patients. Noninvasive blood gas monitoring identified all but 2 patients with respiratory-induced sleep abnormalities. The respiratory arousal rate was correlated with the oxygen desaturation index, but otherwise there were no significant correlations between sleep and nocturnal respiratory parameters. Vital capacity was significantly positively correlated with obstructive apnea index and daytime base excess to nadir oxygen saturation. Inspiratory activity in accessory respiratory muscles was present during REM sleep and/or slow wave sleep in 70% of the patients. Conclusion: The severity of nocturnal respiratory dysfunction is not reflected in the extent of sleep impairment in patients with chronic neuromuscular diseases.

The effect of trunk support on performance during arm ergometry in patients with cervical cord injuries

Earlier studies have shown that the diaphragm might have a postural function that could interfere with its respiratory function during arm cycling in patients with cervical cord injuries with impaired elbow extension. The purpose of this study was to evaluate the effect of trunk support on working performance in such patients. Ten patients with low-cervical-cord injuries performed an arm ergometer test without and with trunk support with at least one week between the tests. The work load averaged 30 (20-50) Watt. Oxygen uptake at steady state averaged 0.71 ± 0.09 1/min without trunk support and 0.64 ± 0.10 1/min with trunk support, P< 0.05. There was no difference in blood lactate without or with trunk support. Maximum performance time averaged 8.3 ± 4.3 min without trunk support and 19.5 ±8.8 min with trunk support, P < 0.01. Oxygen saturation tended to decrease during work and returned to resting values after termination. This study showed that trunk support during arm ergometry in cervical-cord-injury patients with impaired elbow extension decreased the energy cost during sub-maximal work and increased the time to perform work. The results indicate that trunk stabilisation might improve performance of activities of daily living and that it should also be considered during exercise affecting the postural balance of these patients.

Respiratory response to exercise in postpolio patients with severe inspiratory muscle dysfunction

OBJECTIVES To evaluate the limiting factors of exercise performance and to analyze the respiratory strategies adopted during exercise in postpolio patients with severe inspiratory muscle dysfunction. PATIENTS Five patients with prior poliomyelitis associated with scoliosis and with respiratory muscle dysfunction (mean vital capacity, 1.74L [range, 1.1 to 2.4]) were studied at rest and during leg or arm cycle exercise. METHODS Gas exchange was examined by arterial blood gases and mass spectrometry of expired air. Ventilatory mechanics were studied by measurement of esophageal and gastric pressures. RESULTS Blood gases at rest were normal, except for subnormal PO2 levels in three patients. In all but one patient, ventilatory insufficiency was the limiting factor for exercise. A compensatory breathing pattern with abdominal muscle recruitment during expiration was present already at rest in three of the patients. The pressures generated by the diaphragm were below fatiguing margins, ie, levels that in healthy subjects can be sustained for at least 45 minutes. CONCLUSIONS The extent of ventilatory dysfunction was not evident in blood gas values at rest; however, it was revealed by blood gas values during the exercise test. Diaphragm fatigue seems to be avoided at the cost of impaired blood gases.

Diaphragm function in patients with cervical cord injury or prior poliomyelitis infection

Diaphragm function was evaluated in cervical cord injury patients (CCI), 1–3 years after injury (CCI1 - 3) and 10 years or more after injury (CCI⩾10), as well as in a group of prior poliomyelitis infection patients (PPI), requiring intermittent positive pressure ventilation (IPPV) for about 6 h per night. Measurements included transdiaphragmatic pressure swings (ΔPdi) at rest, during maximal inspiratory efforts against closed airways (ΔPdimax) and during sniff manoeuvres (ie maximal inhalation through the nose, ΔPdisniff), vital capacity normalized to age and height (VC%), tidal volume (Vt), relative inspiratory time (Ti/Ttot), breathing frequency (fb), and the tension-time index of the diaphragm (TTdi = ΔPdi/ΔPdimax χ Ti/Ttot). The median VC%pred was 50% in the CCI1-3 group and 57% in the CCI≥10 group, but only 28% in the PPI group. APdimax values were similar for the CCI1-3 (11.8 kPa) and CCI≥10 (11.9 kPa) groups, but were lower (7.1 kPa) in the PPI group. Due to the reduction in ΔPdimax, the PPI group had higher ΔPdi/ΔPdimax values than the CCI groups, however, the TTdi was similar amongst the different groups studied. A submaximal exercise test in five cervical cord injury patients and in five polio patients with similar ΔPdimax, ΔPdisniff and TTdi values at rest revealed clear group differences with respect to force development, in that CCI patients showed significant increases in TTdi, while PPI demonstrated only minor changes. In CCI patients, an increase in ventilation was accompanied by an increase in ΔPdi/ΔPdimax while in contrast, the PPI patients showed no increase in ΔPdi/ΔPdimax. We conclude that CCI patients, both recently and previously injured, have a similar maximal inspiratory force and are less impaired than the PPI patients. The TTdi at rest is similar in all groups, but the PPI patients react to inspiratory loads with little increases in TTdi, while the CCI patients increase their TTdi above fatiguing (0.15) levels. The different behaviours may be linked to loss of sensory pathways in the CCI patients.

Electromyographical evidence for exercise-induced diaphragm fatigue in patients with chronic cervical cord injury or prior poliomyelitis infection

The purpose of this study was to determine, in exercising patients, how much diaphragm force increases before electromyographical evidence of diaphragm fatigue occurs. The study was performed in ten male patients with complete cervical cord injury (CCI) at the C5 to C8 levels, and five male patients with prior poliomyelitis infection (PPI) requiring chronic treatment with intermittent positive pressure ventilation (IPPV) at night. We studied the time course of the diaphragmatic tension-time index (TTdi), the centre frequency (CFdi) of the diaphragm electromyogram (EMGdi) power spectrum, and the ventilatory parameters, during steadystate submaximal arm/leg exercise.During exercise, early signs of diaphragm fatigue were present in seven out of 10 CCI patients and in four out of five PPI patients, as indicated by a reduction in CFdi. The increase in TTdi achieved before reductions in CFdi occurred was twofold in both the CCI and PPI patients. All patients except for the PPI patients, who demonstrated a reduction in CFdi, showed an increase in minute ventilation (VE), achieved by increasing both their tidal volume (Vt) and the breathing frequency (fb). The PPI patients demonstrating reductions in CFdi during exercise also increased their VE however, this was achieved by increasing fb while Vt remained constant. Following the reductions in CFdi, the CCI patients further increased their TTdi throughout the exercise test, while the PPI patients reduced their TTdi values.In conclusion: (1) During exercise, electromyographical evidence for diaphragmatic fatigue frequently occurred in the CCI and PPI patients studied; (2) Compared to the eightfold increase in TTdi seen in healthy subjects before reductions in CFdi occur, the TTdi values increased only two-fold before electromyographical evidence of diaphragm fatigue was present in these patients; (3) There is a clear discrepancy between the CCI and PPI patients who demonstrate electromyographical evidence of diaphragm fatigue, in terms of their ventilatory and TTdi responses.