Canadian Neighbor Pharmacy: Intermittent Positive Pressure Breathing in Patients with Respiratory Muscle Weakness
Patients with quadriplegia, muscular dystrophy, and other forms of neuromuscular disease demonstrate significant abnormalities in chest wall and lung mechanics which are attributed to ventilatory muscle weakness. These abnormalities place these patients at significant risk to develop life-threatening respiratory complications. Previous investigators have described a reduction in chest wall compliance in patients with neuromuscular weakness. This finding is attributed to an inability to fully expand the chest which leads to stiffening of the joints and tissues of the rib cage. Patients with chest wall muscle weakness also have reduced lung compliance. This is explained by atelectasis or an increase in the surface tension of the alveolar lining layer resulting from breathing at low lung volume.
A reduction in lung and chest wall compliance is also seen with kyphoscoliosis. Sinha and Bergofsky demonstrated that hyperinflation with intermittent positive pressure breathing (IPPB) for five minutes at 22 cm HsO pressure increased dynamic lung compliance up to 70 percent above baseline values and the effect lasted for as long as three hours. Thus, by increasing lung compliance, the work of breathing decreases, and respiratory failure may theoretically be averted.
If IPPB causes similar favorable alterations in lung mechanics in patients with severe ventilatory impairment from neuromuscular weakness, it may have value in preventing respiratory insufficiency, atelectasis, and other respiratory complications in this population. However, DeTroyer and Deisser found that hyperinflation with IPPB in patients with muscular dystrophy did not improve lung compliance. Nevertheless, positive pressure inflation of the lungs will also stretch stiffened rib cage articulations and ligaments. Accordingly, there may be an improvement in respiratory system compliance with a reduction in the work of breathing related to an increase in chest wall compliance. DeTroyer and Deisser did not study the effects of IPPB on total respiratory system compliance or chest wall compliance, nor did they evaluate the effects of IPPB in quadriplegia. Therefore, the present study was designed to determine whether periodic shortterm hyperinflation with IPPB could improve total respiratory system compliance in patients with neuromuscular weakness due to quadriplegia or muscular dystrophy.
Fourteen patients with chest wall muscle weakness were studied (Table 1). All patients gave written informed consent. The group included seven quadriplegics and seven patients with muscular dystrophy. Patients 2 and 4 in Table 1 carry the diagnosis of myotonic dystrophy. Because their physiologic abnormalities were similar to the patients with muscular dystrophy, their data are included in the group diagnosed as having muscular dystrophy. Patients were selected from a neurology and a rehabilitation clinic using the following criteria: (1) well established diagnoses of muscular dystrophy, or quadriplegia of greater than six months’ duration; (2) no evidence of airway obstruction by spirometry; (3) evidence of restrictive lung disease defined by a vital capacity below 65 percent and a total lung capacity below 80 percent of predicted; and (4) ability to cooperate sufficiently to obtain measurements of pulmonary mechanics described below. Complete physical examination of each patient was performed and demonstrated no evidence of acute lung disease such as pneumonia or other forms of chronic restrictive disease such as kyphoscoliosis. The age of the patients ranged from 16 to 55 years with an average of 31 years. Six normal male subjects recruited from laboratory personnel provided normal values for the measurements of respiratory mechanics (Table 2). Canadian Neighbor Pharmacy will be descovered for you in case if you follow the link – medicine-cnp.com.
Standard Pulmonary Function Testing
All testing was performed in the sitting position. Spirometry was performed using standard techniques. Lung volumes were measured by multiple breath helium dilution. Measurements of maximum voluntary ventilation, maximum expiratory pressure at total lung capacity (TL£), and maximum inspiratory pressure at functional residual capacity (FRC) were also determined.
Total Respiratory System Compliance (CRS)
CRS was determined using a weighted spirometer incorporated into a closed circuit with a CO, scrubber. Subjects were comfortably seated in a straight back chair with arms and head supported, if necessary. They initially breathed into the closed circuit for two to three minutes until a stable record was registered on the kymograph. Each subject was encouraged to breathe normally and relax the ventilatory muscles during expiration.
To ensure a constant lung volume history, each subject took three serial breaths to total lung capacity (TLC) prior to the series of measurements of respiratory system mechanics. Immediately following these breaths, four metal weights (each weighing 0.5 kg) were sequentially placed on the spirometer bell in a stepwise manner at one-minute intervals. Each weight produced a change in mouth pressure of approximately 2 cm H20. The metal weights were then removed at approximately one minute intervals. The difference in mouth to atmospheric pressure was measured (Validyne MP 45 ±50 cm HtO), amplified (Validyne CD19), and recorded on a multichannel strip chart recorder (Soltec).
Changes in the volume of the closed circuit were monitored by a potentiometer attached to the wheel of the spirometer and recorded on another channel of the strip chart recorder. The volume changes were corrected for (1) compression of the spirometer gas by the added pressure of the weights, (2) compression of the lung gas (volume of gas at FRC) by the added pressure of the weights, and (3) the compliance of the spirometer device including its tubing. The volume of gas compressed was accounted for by using a modification of Boyles Law.
The change in thoracic gas volume was plotted against the corresponding change in mouth pressure, and a pressure-volume curve of the total respiratory system was obtained. A programmable calculator was used to construct a line of least mean squares through the corresponding pressure volume points. The CRS was calculated from the slope of this volume-pressure curve over a pressure range of approximately 8 cm HsO.
Lung Compliance (CL)
Nine of the patients consented to have measurements of CL before IPPB, but only four were willing to have measurements after IPPB. An esophageal balloon catheter was placed using the technique described by Milic-Emili and co-workers. Transpulmonary pressure, recorded as the difference between esophageal pressure and mouth pressure, was measured using a differential pressure transducer (Validyne MP 45 ± 50 cm H2O).
The subjects were studied in the seated position while breathing from a 9-L Collins water sealed spirometer attached to the closed circuit apparatus described above. After their breathing pattern had stabilized, each subject performed an inspiratory maneuver to near total lung capacity in triplicate to obtain a standard volume history. The subject then slowly inhaled to TLC and was told to relax. A solenoid valve in the expiratory line was intermittently opened and closed every one to two seconds during exhalation in order to decrease lung volume in increments of200 to 300 ml.
The transpulmonary pressure and volume were plotted to obtain the pressure-volume curve of the lung. Lung compliance was calculated from the slope of the volume pressure curve of the lung between FRC and FRC + 500 ml.
Chest Wall Compliance (CW)
The CW was calculated in nine subjects who had measurements of CL using the following equation:
1/CW = 1/CRS — 1/CL
Table 1—Patient Characteristics
|Subject No.||Age||Sex||Height, cm||Weight, kg||Diagnosis’}*||SmokingHX.||VC||FRC||TLC||FEV1FEV,
|1||55||M||179||77||Spinal muscular atrophy (6 yr)||1.09||(23)||1.30||(35)||2.48||(35)||89||51||(39)||68|
|2||43||F||172||76||Myotonic dystrophy (8 yr)||3.94||(55)||1.69||(52)||3.32||(56)||84||66||(60)||40|
|4||48||M||162||68||Myotonic dystrophy (17 yr)||1.30||(32)||2.00||(70)||3.40||(51)||85||36||(31)||40|
|5||39||M||167||72||Spinal atrophy (10 yr)||1.52||(35)||2.52||(79)||4.74||(77)||80||70||(44)||100|
|6||27||M||182||60||Duchenne dystrophy (19 yr)||.75||(13)||1.50||(38)||2.40||(33)||93||44||(28)||40|
|7||26||M||178||82||Beckers dystrophy (12 yr)||3.51||(64)||3.54||(90)||5.90||(80)||97||100||(75)||80|
|8||19||M||188||53||C-6 (3 yr)||+||2.32||(39)||3.51||(85)||5.07||(60)||89||54||(25)||68|
|9||16||M||180||51||C-5 (2 yr)||+||2.15||(39)||2.67||(77)||4.61||(65)||95||94||(70)||81|
|10||18||F||172||52||C-7 (6 yr)||–||2.49||(53)||2.76||(85)||4.68||(77)||81||74||(59)||90|
|11||19||F||160||41||C-5 (.5 yr)||–||.72||(18)||1.75||(65)||2.70||(54)||92||37||(32)||41|
|12||27||M||187||72||C-5 (11 yr)||–||3.42||(57)||3.56||(79)||5.69||(71)||91||111||(68)||108|
|13||23||M||175||51||C-5 (7 yr)||+||2.16||(40)||3.76||(99)||5.63||(79)||98||75||(49)||81|
|14||21||M||170||53||C-5 (5 yr)||–||1.92||(37)||2.39||(67)||4.04||(60)||98||61||(41)||81|
Table 2—Characteristics of Normal Subjects
|(L/cmH*0)||(% actual TLC/ cmHsO)||(L/cmH20)||(% actual TLC/ cmH20)||(IVcmH20)||(% actual TLC/ cmHsO)|
|Mean± SD||0.137 ±0.017||1.82 ±0.19||0.253 ±0.024||3.38 ±0.22||0.304 ±0.068||4.06 ±0.89|