Medicare in Canada: a biased view.
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Canada↗
Biomedical subjects
P T Macklem
Publications and source records attributed to P T Macklem.
"Second wind" during inspiratory loading.
Five human volunteers breathed through an inspiratory register to achieve a transdiaphragmatic pressure (Pdi) of 42-45% of the maximum, until fatigue. During the period of resistive breathing all subjects experienced at least one episode of a sudden feeling of relaxation and relief from dyspnea, i.e., "second wind." These episodes were accompanied by a sudden decrease in the neural stimulation to the diaphragm as reflected in the electromyogram (EMG). Changes in lung volume or chest configuration were eliminated as was recruitment of accessory muscles of inspiration during the "second wind"; thus, there appeared to be a change in the contractile function of the diaphragm such that the same force (Pdi) was achieved with less neural input. These results indicate that the phenomenon of "second wind" has physiologic correlates and may be subject to experimental verification and manipulation.
Adult↗
The geometry of the microvascular bed of the diaphragm: comparison to intercostals and triceps.
The diaphragm may differ from other skeletal muscles in certain blood flow characteristics. We attempted to determine if this could be accounted for by structural differences in the microvasculature. We compared coded specimens of the diaphragm to the intercostals and triceps in rats by a cast corrosion, scanning electron microscopic study. For the comparison we first quantitatively described the vasculature by measuring the angles, distances, and diameters. We also tabulated subjective, descriptive, recurring patterns. We then performed frequency analysis by vessel diameter, correlation, and factor analysis to obtain the description. Arteries and veins of greater than 50 microns diameter have structural characteristics of a conducting system, namely, infrequent, single branching at obtuse angles whereas the vessels from about 15 to 50 microns in diameter have greater branching and frequently splay into many smaller streams. The capillaries form arcades and dichotomize with Y- and psi-shaped branches. The best predictor of branching (distance, angle, and pattern) is the trunk diameter. Individual and combinations of measurements and patterns comparing the diaphragm to the triceps and intercostals pointed out no convincing difference in these structural aspects of microvasculature of these muscles.
Animals↗
Effect of caffeine on skeletal muscle function before and after fatigue.
We studied the effect of caffeine on voluntary and electrically stimulated contractions of the adductor pollicis muscle in five adult volunteers. Caffeine (500 mg) was administered orally in a double-blind fashion. Electrical stimulation of the ulnar nerve was performed at 10, 20, 30, 50, and 100 Hz before and after a sustained voluntary contraction held at 50% of the maximal voluntary contraction (MVC). A brief tetanus at 30 Hz was also performed to calculate relaxation rate in the fresh muscle. Contractile properties, relaxation rate, and endurance were then assessed after caffeine and placebo, as well as the response of the fatigued muscle to different frequencies of stimulation. There was no difference in the maximal tension obtained with electrical stimulation (T100) or in the MVC between placebo and caffeine. The tensions developed with electrical stimulation at lower frequencies increased significantly with caffeine ingestion, shifting the frequency-force curve to the left, both before and after fatigue. Mean plasma caffeine concentration associated with these responses was 12.2 +/- 4.9 mg/l. We conclude that caffeine has a direct effect on skeletal muscle contractile properties both before and after fatigue as demonstrated by electrical stimulation.
Adult↗
A model of inspiratory muscle mechanics.
We have previously shown that the costal and crural parts of the diaphragm have different actions on the rib cage (RC) and that the tension developed in one part is not transmitted perfectly to the other. Thus the diaphragm can be modeled pneumatically or electrically as two generators or pumps in series between the lung and abdomen. As such, the force developed by diaphragmatic contraction is the sum of the forces developed in each part, whereas the volume displaced is the same for each part and equal to the total volume displaced. The costal part of the diaphragm is in series with the intercostal and accessory (IA) muscles between the lung and RC, whereas the crural part is in parallel. The volume displaced by simultaneous contraction of the crural part and IA is the sum of volumes displaced by each part. The action of pleural and abdominal pressure [acting through the area of apposition (Aap) of the diaphragm to RC] can be modelled as a summing junction between IA and RC. With hyperinflation the costal part acts more and more in parallel with both IA and the crural part, whereas Aap diminishes, so that the ability to develop large forces decreases independently of the muscles' force-length relationships. The model also predicts that the factors determining the length of the costal and crural parts are different. Finally, the parallel and serial arrangement of the inspiratory musculature allows for increases in maximum power, maximum force, and maximum velocity by appropriate recruitment of the various muscle groups.
Biomechanical Phenomena↗
Non-adrenergic inhibitory nerves.
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Animals↗
[Relationship between reduced pulmonary elasticity in smokers and peripheral airway obstruction and pulmonary emphysema].
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Adult↗
Nonpurinergic nature and efficacy of nonadrenergic bronchodilation.
The nonadrenergic inhibition of airway smooth muscle was investigated in vivo in the anesthetized cat. We examined 1) the bronchodilatating nature of the selective purinergic agonists [adenosine (AD) and adenosine triphosphate (ATP)], 2) antagonistic nature of aminophylline and quinidine, and 3) the comparative efficacy of nonadrenergic and sympathetic inhibition in reversing bronchoconstriction induced with serotonin. Alterations in smooth muscle tone were studied via electrical stimulation of the vagus nerves and measurements of pulmonary resistance. We found that neither AD nor ATP, aerosolized or injected, altered the tonic bronchoconstriction. Dipyridamole, an AD reuptake inhibitor, did not alter the response to AD, ATP, or electrical stimulation. Both aminophylline and quinidine block nonadrenergic dilatation at high dose levels (69 and 29 mg/kg, respectively); further, both reputed antagonists impair cholinergic excitation. Nonadrenergic inhibition is equipotent to sympathetic inhibition in reversing bronchoconstriction; however, nonadrenergic inhibition is more prolonged (4.0 +/- 1.8 min). We conclude that probably neither ATP nor AD is the neurotransmitter for nonadrenergic bronchodilatation in the cat, and that nonadrenergic inhibition is both potent and long lasting.
Adenosine↗
Action of costal and crural parts of the diaphragm on the rib cage in dog.
We studied the action of the costal and crural (vertebral) parts of the diaphragm on the lower rib cage in normal supine dogs. The two parts of the diaphragm were separately stimulated by electrodes directly implanted in the muscle or via the different phrenic nerve roots in the neck. The results of the experiments indicate the following. 1) The costal and crural parts of the diaphragm have a different segmental innervation and a different mechanical action on the rib cage. 2) The costal diaphragm expands the lower rib cage when it contracts. This rib-cage expansion is due mostly to the fulcrum of the abdominal contents and partly to the rise in abdominal pressure that takes place during diaphragmatic contraction. The pericardial attachments play no role in this action of the diaphragm. 3) The action of the crural diaphragm on the lower rib cage depends only on the balance between the inspiratory force exerted by the rise in abdominal pressure and the expiratory force exerted by the fall in pleural pressure. In the intact animal at functional residual capacity, these two opposite effects cancel each other. 4) The inflationary action of both parts on the rib cage decreases progressively as lung volume increases. The findings also suggest that the rise in abdominal pressure which occurs when the diaphragm contracts expands the lower rib cage by acting through the area of apposition of the diaphragm to the rib cage. These findings also strengthen the idea that the diaphragm actually consists of two muscles.
Abdomen↗
Changes in EMG power spectrum (high-to-low ratio) with force fatigue in humans.
During and following high-load fatiguing voluntary contractions, the force response of skeletal muscle to electrical stimulation is altered so that the frequency-force curve is moved to the right. Fatiguing contractions also result in a shift to the left of the electromyographic (EMG) power spectrum. In the quadriceps muscle and the diaphragm of normal subjects the change in the force response to electrical stimulation has been correlated with the EMG changes. After repeated submaximal contractions in the quadriceps and diaphragm, the forces produced by electrical stimulation at low frequencies were reduced, indicating low-frequency fatigue. This type of fatigue persisted for several hours but did not result in any change in the EMG high-to-low ratio. Low-frequency fatigue is probably an important aspect of the failure of skeletal muscle to generate adequate force, and the EMG high-to-low ratio may not recognize this type of fatigue.
Diaphragm↗
The oxygen cost of breathing in patients with cardiorespiratory disease.
We measured the oxygen cost of breathing (VO2resp) in 13 patients with cardiorespiratory disease requiring artificial ventilation as the difference between the oxygen consumption during spontaneous respiration (VO2tot) and that during artificial ventilation (VO2nonresp). Average VO2tot was 312 +/- 90 ml/min (mean +/- 1 SD), whereas VO2nonresp was 246 +/- 38 ml/min (p less than 0.01). Average VO2resp was 75 +/- 82 ml/min (range, 8 to 286), representing 24% of VO2tot or 8.7 +/- 8.9 ml O2/L ventilation. In normal resting adults, VO2resp in 5 to 10 ml/min, about 1 to 3% VO2tot, or 0.25 to 2.5 ml O2/L ventilation. The VO2resp had an exponential relationship with FEV1 (r = 0.97) in 6 patients who had had prior spirometry. Because minute ventilation was normal in our patients (8.8 +/- 2.2 L/min), the elevated VO2resp represented an increase in the work of breathing as well as a decrease in the efficiency of the respiratory muscles. These results suggest that, where O2 transport is compromised, artificial ventilation may release substantial quantities of oxygen for use by other body systems.
Adult↗
Correlation of regional breath sound with regional ventilation in emphysema.
We measured regional breath sound intensities (Ib) by a microphone amplifier system in 8 subjects with emphysema. We also measured regional white noise transmissions (Tn) from the same areas in all subjects. The recorded areas were 5, 10, 15, and 20 cm from the apex of the lung just lateral to the right anterior midclavicular line. Xenon ventilation indexes (xenon tidal raw counts, an index of total regional ventilation; xenon equilibration raw counts, an index of ventilating lung volume; xenon ventilation per unit volume (Vr), an index of ventilation per unit volume) were also recorded from the same areas. The Ib, Tn, Ib/Tn (an index of sound generation), and xenon ventilation indexes were all expressed as a fraction of the mean value of all four recorded areas. The Ib and Ib/Tn correlated best with the xenon tidal raw counts, correlated well with the xenon equilibration raw counts, and correlated poorly with Vr. We conclude that Ib and Ib/Tn can be used to quantify regional ventilation in subjects with emphysema.
Auscultation↗
The effects of inspiratory muscle training in patients with cystic fibrosis.
This study evaluated whether inspiratory muscle training (IMT) could increase inspiratory muscle strength and endurance and exercise performance in 11 patients with cystic fibrosis (CF) with moderately severe airflow limitation. The IMT consisted of breathing through an inspiratory resistance (IR) for 15 min twice daily for 4 wk, preceded or followed by a 4-wk control period. After IMT, there was an increase in inspiratory muscle strength measured by maximal inspiratory mouth pressure at functional residual capacity: 74 +/- 18 cmH2O before training to 81 +/- 12 cmH2O after training, mean +/- 1 SD, p less than 0.025, and in inspiratory muscle endurance measured by the maximal IR tolerated for 10 min. Limitation of performance in the progressive exercise test was related to increased airflow limitation and possibly to poor nutrition. Mean exercise performance during progressive or submaximal exercise testing did not change after training. It is concluded that this form of IMT improved inspiratory muscle strength and endurance, but had little effect on exercise performance in patients with CF.
Adolescent↗
Clinical manifestations of inspiratory muscle fatigue.
Twelve patients exhibiting difficulties during discontinuation of artificial ventilation permitted us to investigate physical examination techniques used in diagnosing inspiratory muscle fatigue. Diaphragmatic and intercostal electromyographic tracings, arterial blood gases, rate and depth of ventilation, and thoracoabdominal motion were monitored during spontaneous breathing. Six patients showed electromyographic evidence of inspiratory muscle fatigue. A sequence of events leading to respiratory acidemia emerged--namely electromyographic evidence of fatigue, accompanied or followed by an increased respiratory rate, in turn followed by alternation between abdominal and rib cage breathing (respiratory alternans), paradoxical inward abdominal motion during inspiration (abdominal paradox), and finally an increase in PaCO2 associated with a fall in minute ventilation and respiratory rate, and worsening of respiratory acidemia. The abnormalities of respiratory movements may be reliable clinical signs of inspiratory muscle fatigue, particularly when accompanied by tachypnea and hypercapnia.
Adult↗
The diaphragm in health and disease.
The diaphragm consists of two separate muscles, the costal and crural parts, with different segmental innervation and different action on the rib cage. Diaphragmatic endurance is determined by the balance between energy supply and demand. Both an increase in demand and a decrease in supply of energy lead to diaphragmatic fatigue. Under conditions of reduced O2 transport to the body, the inspiratory muscles may command a disproportionate amount of the total body O2 consumption, particularly if the work of breathing is increased. Their energy demands may thus contribute significantly to the pathogenesis of cardiogenic shock and lactic acidosis. Inspiratory muscle fatigue can be diagnosed by observing and palpating: (1) abdominal paradox, a fall in abdominal pressure and an inward displacement of the abdomen during inspiration, and (2) respiratory alternans, a variation in abdominal pressure changes from breath to breath, reflected in variations in the inspiratory movements of rib cage and abdomen. Treatment consists in decreasing energy demands and increasing supplies. Artificial ventilation should be considered to accomplish the former. Methyl xanthines improve diaphragmatic contractility and specific diaphragmatic training programs improve diaphragmatic endurance.
Acidosis↗
Aminophylline improves diaphragmatic contractility.
In an attempt to explain the clinical efficacy of aminophylline, we studied its effect on diaphragmatic function in eight normal subjects. The relation between the electrical activity of the diaphragm and the pressure generated by the diaphragm was assessed during voluntary contractions before and after aminophylline infusion. Aminophylline shifted the electrical activity/pressure curve to the left; the pressure at a given electrical activity increased an average of 15 per cent (P less than 0.001). In four subjects, pressure was also measured during stimulation of the phrenic nerve at various frequencies before and after diaphragmatic fatigue was produced by resistive breathing, with and without aminophylline infusion. Pressure increased after fatigue at all stimulation frequencies with aminophylline, as compared with the pressure after identical fatigue runs at the same stimulation frequencies without aminophylline. The mean plasma aminophylline concentration associated with these responses was 13 +/- 0.9 mg per liter. We conclude that aminophylline improves the diaphragm's contractility and renders it less susceptible to fatigue.
Adult↗
The diaphragm: two muscles.
The costal and crural parts of the diaphragm were separately stimulated in anesthetized dogs. Stimulation of the costal part increased the dimensions of the lower rib cage, whereas stimulation of the costal part decreased the dimensions of the lower rib cage. It is concluded that the diaphragm consists of two muscles that act differently on the rib cage.
Abdomen↗