Breath Interval Research Articles

Monitoring of breathing intervals in narcotic sedation

Monitoring of breathing intervals in narcotic sedation

Effects of chronic hyperglycemia on electrocortical activity states in unanesthetized fetal lambs

Electrocortical activity (ECoG), tracheal pressure and nuchal muscle activity were recorded in utero in 8 chronically hyperglycemic and 10 control unanesthetized fetal lambs to investigate the effects of chronic hyperglycemia on fetal electrocortical activity states. The chronically hyperglycemic state, induced by alloxan administered to the ewes, existed for at least 40 days prior to the experiments. The mean duration of episodes of high voltage (HV) ECoG was significantly increased in the hyperglycemic group (mean ± SD: 21.8 ± 9.2 min) compared with the control group (14.8 ± 3.3 min), but the incidence of low voltage (LV) ECoG was not different between the groups. ECoG power spectra were not different between the groups. During LV ECoG, the proportions of time with neck movements were significantly less in the hyperglycemic than in the control group. No difference in percentages of time with long neck muscle activity was seen during the HV state in both groups. The incidence of breathing movements was equal in both groups, during HV as well as LV ECoG. No differences in breathing interval were observed.

Value of observation of fetal breathing activity in antenatal assessment of high-risk pregnancy

While observation of fetal breathing movements has been used in fetal assessment, quantitative parameters (percent time spent in breathing [incidence], breath rate, or breath rate variability) have not been adequately evaluated as predictive tools. We examined 283 patients with high-risk pregnancies between 32 and 42 weeks' gestation and correlated their fetal breathing movement parameters with the rates of perinatal mortality, intrapartum fetal distress, neonatal acidosis, low 5-minute Apgar score, and intrauterine growth retardation. Fetal breathing data from standardized 60-minute biophysical tests were analyzed and compared with our institutional standards. Parameter values greater than 2 SD from the means of a previously studied normal population were considered abnormal. Whereas no individual parameter was a highly accurate predictor of adverse outcome, a fetal breathing movement incidence of less than 5% provided the best cutoff for diagnostic accuracy. Seventy percent of fetuses with 30 minutes of apnea had normal outcomes, whereas abnormally high breath rates (greater than 60 breaths/min) and low breath rates (less than 33 breaths/min) occurred with equal frequency among normal and pathologic fetuses. Breath interval variability was of no benefit in detecting fetuses with poor outcomes. Observation of fetal breathing movement incidence appeared to be most effective in pregnancies complicated by chronic hypertension and least effective in those with preeclampsia.

Delayed appearance of blood lactate with reduced frequency breathing during exercise.

The purpose of the present study was to investigate the blood lactate (LA-) responses to hypoventilation induced by reduced frequency breathing (RFB) during recovery from exercise. Five male subject performed 16 4 min cycling bouts alternating with 16 min rest periods. Exercise intensities were chosen at power outputs corresponding to 30% VO2max at 2 mMLA-, VO2 at 4 mMLA-, and 90% VO2max in each subject. Breathing frequency was voluntarily controlled starting 10 s before each 3rd min of exercise and maintained throughout the rest of the exercise period. Four different breathing patterns at each exercise intensity were used: normal breathing (NB), breathing every 4 s, breathing every 8 s, and maximal RFB. Except for the NB trials, subjects held their breath at functional residual capacity during each breathing interval. The concentration difference of LA- between the 3rd min sample and the 4th min sample was defined as the lactate change during exercise (delta LA-ex), and that between the 4th min sample and the sample at the 3rd min after the end of the exercise as the lactate change during recovery (delta LA-rec). An ANOVA showed significant (p less than 0.05) differences in breathing procedures only in delta LA-rec. delta LA-rec seemed to increase as compared to NB only at VO2 at 4 mMLA- and 90% VO2max, while delta LA-ex remained unchanged as compared to NB in spite of reduced VA. These results might indicate that RFB inhibited lactate removal from working muscles during exercise.

Effects of hypercapnia and hypoxemia on fetal breathing after decortication.

The effects of hypercapnia and hypoxemia on breathing movements were studied in 12 chronically decorticated fetal sheep, 127-140 days gestation. The fetal state of consciousness was defined in terms of activity of the lateral rectus and nuchal muscles. Arterial blood pressure was monitored. Fetal breathing was determined by integrated diaphragmatic electromyogram (EMG) and analyzed in terms of inspiratory time (TI), expiratory time (TE), electrical equivalent of tidal volume (EVT), breath interval (TT), duty cycle (TI/TT), mean inspiratory flow equivalent (EVT/TI), and instantaneous ventilation equivalent (EVT/TT). Fetal breathing occurred only during episodes of rapid-eye movements, and the response to hypercapnia consisted of an increase in EVT, TI, EVE, and EVT/TI and a decrease in the coefficient of variation of all measured parameters. Induction of hypoxia during episodes of spontaneous fetal breathing produced a decrease in the rate of breathing and an increase in EVT and TI with no change in the variability of all parameters studied. Since similar responses to hypercapnia and hypoxemia are seen in the intact fetus, we conclude that the cerebral cortex has no obvious effect on the chemical control of fetal breathing.

Maternal dietary substrates and human fetal biophysical activity: I. The effects of tryptophan and glucose on fetal breathing movements

To study the effects of l-tryptophan and glucose on fetal breathing activity, we examined 40 women with normal term pregnancies, randomly assigned to four equal groups who either continued fasting (group C), received 1 gm of oral tryptophan (group T), received 100 gm of oral glucose (group G), or received both substrates (group T + G). Studies lasted 210 minutes, during which fetal breathing movements were observed with real-time ultrasonography and entered and analyzed for incidence, rate, and variability on a microcomputer. Plasma glucose and tryptophan levels were determined every 30 minutes. The incidence of fetal breathing movements declined in group C and rose significantly in the other groups. Breathing rates were unchanged in groups C and T but rose significantly in groups G and T + G during peak breathing intervals. Breath interval variability did not change significantly in any study group. Maternal administration of tryptophan is associated with an alteration in fetal breathing activity but to a lesser degree than that observed after maternal glucose loading.

Maternal dietary substrates and human fetal biophysical activity

Abstract To study the effects of l-tryptophan and glucose on fetal breathing activity, we examined 40 women with normal term pregnancies, randomly assigned to four equal groups who either continued fasting (group C), received 1 gm of oral tryptophan (group T), received 100 gm of oral glucose (group G), or received both substrates (group T + G). Studies lasted 210 minutes, during which fetal breathing movements were observed with real-time ultrasonography and entered and analyzed for incidence, rate, and variability on a microcomputer. Plasma glucose and tryptophan levels were determined every 30 minutes. The incidence of fetal breathing movements declined in group C and rose significantly in the other groups. Breathing rates were unchanged in groups C and T but rose significantly in groups G and T + G during peak breathing intervals. Breath interval variability did not change significantly in any study group. Maternal administration of tryptophan is associated with an alteration in fetal breathing activity but to a lesser degree than that observed after maternal glucose loading.

The bronchodilator effect of a fixed-combination metered aerosol (fenoterol and ipratropium bromide).

The fixed-combination metered aerosol lK6 (fenoterol 0.05 mg/puff, ipratropium bromide 0.02 mg/puff--Berodual, Boehringer-Ingelheim Ltd., Ridgefield, Conn.) was administered to 12 children (8 boys, 4 girls) aged 3 1/2 to 6 2/12 years who had extrinsic bronchial asthma. Three forms of administration, each with a different site of action, were compared: Two puffs during inspiration. Probable site of action: oral cavity, pharynx, larynx, trachea, and bronchi. Two puffs using an inhalational aid during inspiration. Probable site of action: pharynx, larynx, trachea, and bronchi. Two puffs in the breathing interval after deep inspiration. Probable site of action: oral cavity and pharynx. The resistance of the respiratory system (Rrs) was measured using oscillometry for up to 360 minutes after administration. A significant decrease of the median resistance was found with all three forms of administration. The changes were Form 1-48% of baseline after 120 minutes; Form 2-47.9% of baseline after 60 minutes; Form 3-44.4% of baseline after 30 minutes. The greatest decrease was observed with form 1. The study indicates that significant bronchodilation was achieved in small children using the combination of fenoterol and ipratropium bromide administered by metered aerosol even when inhalation and the release of the puff were not synchronized. A significant bronchodilator effect was also observed in cases of severe bronchial obstruction in which transport of the active ingredients to the lower airways could not be sufficiently guaranteed.

Low-concentration Oxygen Therapy Via a Demand Oxygen Delivery System

Recent heightened concern about the costs of medical care has stimulated research and development in devices and schemes for saving costs while retaining quality of care. Consistent with that concern is the fact that standard steady-flow oxygen delivery is so wasteful. Almost its entire benefit occurs at the very beginning of inspiration. We compared the efficacy of nasal oxygen delivery via a new demand oxygen delivery system (DODS) with the standard steady-flow (SF) method. The DODS incorporates a valve and sensor interposed between the oxygen reservoir and the patient, which meters oxygen to the patient only during early inspiration. Twelve COPD subjects with hypoxemia at rest received oxygen at flow settings of 1 to 4 L/min via SF and at various breath interval settings via the DODS method, calculated to match the above spectrum of the SF. We measured oxygen delivery using an ear oximeter. The results indicate that significantly less oxygen was required to provide equivalent saturations using the DODS compared with the SF method (p less than .001). The mean comparative savings in oxygen is better than seven to one favoring the DODS over the SF method. Further study is warranted, since the widespread use of such a device could result in substantial cost saving while increasing the range of portable oxygen delivery.

Respiratory and heart rate patterns in infants destined to be victims of sudden infant death syndrome: average rates and their variability measured over 24 hours.

From a prospective study in which 24 hour recordings of the electrocardiogram and respiratory activity (abdominal wall movement) were made on a population of full term infants, 22 recordings were obtained from 16 infants who later were victims of the sudden infant death syndrome. The average heart rate, average heart rate variability, average breath to breath interval, and average breath to breath interval variability over the whole of each recording for the 22 recordings were compared with those from a control group of 324 infants selected at random from the rest of the population. No significance was found in the number of recordings from those infants who suffered the sudden infant death syndrome which lay outside the 5th-95th percentile range of the control group for the four variables studied. In a group comparison no difference was found between the sudden infant death syndrome group and the controls either in terms of the respiratory variables studied or in terms of the average heart rate variability. The results did, however, suggest that there may be a group difference in terms of the average instantaneous heart rate.

The effects of maternal hyperoxia on fetal breathing movements in third-trimester pregnancies

Fetal breathing movements and gross fetal body movements were observed before, during, and after maternal hyperoxia induced by inhalation of 50% oxygen in 14 women with normal term pregnancies. Studies were performed with real-time B-scan linear-array ultrasound and were standardized for time of day, maternal nutritional status, postprandial interval, and length of observation. Each study included a 30-minute baseline, followed by 15 minutes of hyperoxia, and 45 minutes of continued monitoring. No significant changes occurred in the mean incidences of fetal breathing movements, gross fetal body movements, the mean breathing rate, or breath interval variability, as analyzed in 5-minute epochs. Maternal Po2, as measured by transcutaneous electrodes, increased to the maximum level after 5 minutes of hyperoxia (155% over control levels). The breathing activity of normal third-trimester fetuses appears to be stimulated maximally in the second and third postprandial hours and cannot be further increased by maternal hyperoxia. This protocol represents a possible clinical strategy for investigating fetuses at risk for intrauterine hypoxia, provided that similar experimental conditions are maintained.

Tourniquet effects on muscle oxygen tension in dog limbs. Experiments with cooling and breathing intervals.

The effects of repeated tourniquet applications with breathing periods on muscle pO2 was studied in adult dogs. A tourniquet was applied to one hind limb. The tourniquet was repeatedly inflated for 1 h; four ischemic periods were separated by 20-min recirculation intervals. In other series the limb was cooled prior to tourniquet application, or the animal was treated with the proteinase inhibitor Trasylol. Following tourniquet deflation, the pO2 value in the gastrocnemius muscle initially increased, reaching a peak within 5 min. This initial increase became less apparent with repeated periods of ischemia as well as with prolongation of the ischemic period. The results indicate that cooling prior to tourniquet application represents a better technic than the use of breathing periods or Trasylol.

Ultrasonic measurement of rate and depth of human fetal breathing: Effect of glucose

A recently developed ultrasonic tracking device was used to determine the effect of maternal intravenous glucose infusion on amplitude and frequency of breathing movements in six healthy human fetuses at 38 to 40 weeks' gestation. Following a 2-hour observation period, an intravenous injection of either 25 gm of a 50% glucose solution or an equal volume of saline was given to the mother. Observations were continued for a further 4 hours. Fetal rib cage and abdominal diameters were measured continuously with the ultrasonic tracking device and the information was recorded on a strip chart recorder for later analysis. Breath interval and incidence measurements were highly correlated with data obtained by an independent technique (r ≥ 0.90). During the first 80 minutes after glucose injection, total fetal trunk movement recorded during breathing movements increased from 1.5 ± 0.2 to 2.9 ± 0.4 mm (P < 0.05). There was no significant change in the frequency or variability of fetal breathing movements after glucose infusion.

Human sinus arrhythmia as an index of vagal cardiac outflow

Since changes of heart period follow changes of cardiac vagal efferent activity quantitatively with nearly fixed latencies, measurements of respiratory sinus arrhythmia may provide insights into human central vagal mechanisms. Accordingly, I measured intervals between heartbeats during controlled breathing (at breathing intervals of 2.5-10 s and nominal tidal volumes of 1,000 and 1,500 ml) in six healthy young men and women. As breathing interval increased, the longest heart periods became longer, the shortest heart periods became shorter, and the peak-valley P-P intervals increased asymptotically. Peak-valley P-P intervals also increased in proportion to tidal volume. However, this influence was small: a 50% increase of tidal volume increased the average peak-valley P-P interval by only about 15%. The phase angles between heart period changes and respiration varied as linear functions of breathing interval. Heart period shortening (cardioacceleration) began in inspiration at short breathing intervals and in expiration at long breathing intervals. Heart period lengthening, however, began in early expiration at all breathing intervals studied. These results point toward a close relationship between variations of respiratory depth and interval and the quantity, periodicity, and timing of vagal cardiac outflow in conscious humans. They suggest that, at usual breathing rates, phasic respiration-related changes of vagal motoneuron activity began in expiration, progress slowly, and are incompletely expressed at fast breathing rates.

Effects of hypercapnia on tracheal pressure, diaphragm and intercostal electromyograms in unanaesthetized fetal lambs.

1. The electromyographic (e.m.g.) activity of the diaphragm and intercostal muscles has been recorded during breathing movements of unanaesthetized lambs in utero (109-135 days), and compared with the changes of tracheal pressure.2. The diaphragm e.m.g. was irregular in size, shape and timing, with a variable rate of rise during inspiration, often with a flattening of integrated activity before the end of a breath and with little or no post-inspiratory activity.3. The diaphragm e.m.g. gave the most reliable measurements of breath interval and incidence: in eucapnia mean T(I) was 0.45+/-0.02 (S.E. of mean) and T(E) was 0.74+/-0.05 sec, and 58-100% of the diaphragm bursts were associated with identifiable and appropriate changes of tracheal pressure.4. During fetal hypercapnia, produced by increasing the maternal inspired CO(2) in a single change or series of step changes, tracheal pressure amplitude and its rate of change during inspiration increased progressively over the P(a, CO2) range of 37-87 mmHg.5. In eucapnia the area, amplitude and inspiratory slope of the integrated diaphragm e.m.g. were not always correlated with tracheal pressure amplitude, and in hypercapnia they increased only in the lower part of the P(a, CO2) range. Inspiratory intercostal activity increased progressively as the P(a, CO2) was raised.6. The frequency histograms of variables derived from the tracheal pressure, diaphragm and intercostal e.m.g.s were skewed to the left in eucapnia but became normalized during hypercapnia. The rate and depth of breathing became regular.7. The response to mild asphyxia was a combination of the responses to hypercapnia and hypoxia.8. The interpretation of the tracheal pressure and diaphragm e.m.g. as measures of the ;depth' of breathing and respiratory ;drive' in the fetal lamb is discussed.

The pattern of stimulated breathing in man during non-elastic expiratory loading.

1. The pattern of breathing expressed as the relationship between tidal volume and the components of breath interval was studied in normal subjects during CO2 rebreathing, both under unloaded conditions and following the introduction of a non-elastic expiratory resistance. 2. Under unloaded conditions end-expiratory thoracic gas volume (FRC) measured plethysmographically did not alter during the course of the rebreathing experiment. Maximum tidal volume attained (VT, max.) was equal to or just less than the inspiratory capacity of the subject measured at rest. Expiratory reserve volume was not encroached upon even at the highest levels of ventilation. 3. Under loaded conditions the pattern of breathing was altered. VT, max. was diminished in all subjects and FRC showed a progressive rise during rebreathing which was proportional to the resistive load afforded by the artificial resistance. There were no consistent differences in the components of breath duration either at rest or on maximal ventilatory stimulation between the loaded and unloaded states. 4. It is suggested that the pattern of breathing adopted under conditions of expiratory non-elastic loading is influenced more by the secondary effects of breathing at an elevated lung volume, than by the effect of the non-elastic load per se.

Gas exchange and control of breathing in the electric eel, Electrophorus electricus

1. The electric eel Electrophorus electricus is an obligate air breather. Its mouth is structurally adapted for air breathing by an extensively diverticulated and richly vascularized oral mucosa. Air is regularly taken into the mouth and later expelled at the opercular openings. The present investigation concerns the respiratory properties of blood, the dynamics of gas exchange and the control of breathing in the electric eel. 2. Fishes were anesthetized and catheters implanted for sampling of gas in the mouth and blood from the jugular vein draining the mouth respiratory organ, and from a systemic artery. A blood velocity transducer was implanted on the ventral aorta. Following recovery, gas from the mouth, blood gases, blood pH as well as other respiratory and circulatory parameters, were monitored during normal breathing cycles and in response to low and high oxygen tensions in both the aquatic and aerial environment surrounding the fish. In addition, the fish were exposed to a CO2 enriched environment. 3. Table 2 summarizes the respiratory properties of blood. The high oxygen capacity and oxygen affinity may be an adaptive measure against the mixed conditions of arterial blood. The oxygen capacity was largely unaffected by CO2. 4. Electrophorus showed arterial CO2 tensions higher than for typical aquatic breathers and other air breathing fishes studied. PCO2 is increased due to the shunting of blood from the mouth organ to the venous side of the systemic circulation. For the same reason arterial oxygen tensions are normally much below the P100 value. The blood bicarbonate concentration is higher than in typical aquatic breathers. 5. The gas exchange ratio was very low for the mouth respiratory organ and tended to decrease still further in the intervals between air breaths. The gills and/or skin are hence important for CO2 elimination. 6. The interval between air breaths rarely exceeded two minutes in intact free-swimming fish surrounded by aerated water and normal ambient air. The fish was irresponsive to changes in oxygen and CO2 tensions in the water, but breathing of hypoxic and hypercarbic atmospheres caused marked and very prompt increase in the rate of air breathing. Inhalation of a hyperoxic atmosphere caused a depression of air breathing. 7. Heart rate and cardiac output values were higher than earlier reported values for fish. Calculations showed that marked changes occured in the fractional distribution of the cardiac output related to the phase of the breathing cycle and the oxygen tension in the mouth organ. 8. When long intervals prevailed between air breaths the heart rate and cardiac output declined late in the breath interval. Inflation of the mouth organ with oxygen or nitrogen both prompted cardioacceleration and increased blood flow. The changes were of reflex nature and caused by pressure or tension changes inside the mouth.

The measurement of intrapulmonary mixing in children

T K E A L V E O L A R GAS in a normal person breathing room air contains 80 per cent of nitrogen. Cournand 1 in 1941 showed that in normal adults breathing 100 per cent oxygen, the nitrogen present will be washed out, so that after 7 minutes, less than 2 per cent of nitrogen remains in the alveolar air. In adults with chronic obstructive pulmonary disease, there are areas of lungs which are poorly ventilated, so that nitrogen is not removed as rapidly. In these patients more than 2 per cent of nitrogen remains after 7 minutes. This value reflects the nonuniformity of distribution of the inspired air and is called the index of intrapulmonary mixing. Because 7 minutes is a relatively long interval for a young child to remain seated, concentrating, with a mouthpiece held tightly between his lips, it is not as satisfactory for use in pediatric respiratory disease as it is in adult medicine. Accordingly, a study was attempted to modify the method for use in children in a group ranging in age from 6 to 12 years. The data indicate that the pulmonary emptying rate is shorter in children than adults and that a 2 minute breathing interval is all that is required.