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Biomedical subjects

O P Mathew

Publications and source records attributed to O P Mathew.

At least 37 records · Page 2Linked to original sources
PubMed1991

Afferent activity in the external branch of the superior laryngeal and recurrent laryngeal nerves.

We investigated the presence of respiratory-modulated receptors in the recurrent laryngeal nerve (RLN) and the external branch of the superior laryngeal nerve (ExtSLN) in anesthetized, spontaneously breathing dogs. Of 39 receptors recorded from the ExtSLN, the vast majority responded with a slowly adapting discharge to compression of the cricothyroid muscle, and only 1 responded to probing of the laryngeal mucosa. Ten receptors showed a respiratory modulation. All 30 receptors recorded from the RLN responded to probing of the laryngeal lumen, most of them (60%) with a rapidly adapting response. Seven of the slowly adapting receptors exhibited a respiratory modulation; 38% of the receptors tested were stimulated by water, and only 15% by smoke. No receptors stimulated by laryngeal cooling were identified in either nerve. Our study indicates that in the RLN and the ExtSLN there are relatively few afferents responding to changes in transmural pressure and mechanical irritation, as compared to the internal branch of the SLN. The relative scarcity of receptors responding to transmural pressure and irritant stimuli is consistent with previous observations in dogs that indicate a preponderant role for afferents in the internal branch of the SLN in the reflex responses to laryngeal stimulation.

Afferent Pathways↗
PubMed1990

Determinants of milk flow through nipple units. Role of hole size and nipple thickness.

The aim of the present study was to elucidate the role of hole size and thickness in determining milk flow through nipple units during bottle feeding. Commonly used standard nipple units (SMA single-hole, Enfamil single-hole, and Twist-on) for term and preterm infants, as well as Nuk-type nipple units (SMA Nuk, Enfamil Natural, and Nuk) were tested. The size of the nipple hole and wall thickness were determined for each nipple unit. Airflow was measured by forcing pressurized air through the feed hole. Simulated sucks were used to measure the milk flow. A marked variability in airflow and milk flow was observed within and among the various types of nipple units studied. Within each type of nipple unit, both milk flow and airflow measurements correlated well with hole size. The thickness of the nipple units contributed minimally to the observed variability. We conclude that differences in hole size primarily account for the observed variability in milk flow. This finding may be clinically important in that rapid milk flow can lead to apnea and bradycardia in some preterm infants. The above observations imply that design changes are necessary to reduce the variability of milk flow within each nipple type. Moreover, milk-flow measurements made using a simple mechanical system and airflow measurements used by the industry are equally sensitive to evaluate nipple flow.

Animals↗
PubMed1990

Carbon dioxide-responsive laryngeal receptors in the dog.

The purpose of this study was to relate the carbon dioxide (CO2) response of laryngeal receptors to their behavior during the breathing cycle (i.e. their response to transmural pressure changes, laryngeal movement or decreases in temperature) or during exposure to irritant stimuli (water or cigarette smoke). In 9 anesthetized mongrel dogs breathing spontaneously through a tracheostomy, unit activity from the superior laryngeal nerve was recorded while warmed and humidified gas mixtures (air or 10% CO2 in O2) were passed, for 1 min, through the functionally isolated upper airway in the expiratory direction. None of the 10 cold receptors studied were affected by CO2. Eleven of 20 laryngeal non-modulated mechano-receptors were stimulated (from 0.3 to 1.6 imp/sec) by exposure to CO2. These CO2-responsive receptors were also stimulated by known irritant stimuli (cigarette smoke, water), although not all receptors which responded to these irritants were stimulated by CO2. Twelve of 33 respiratory-modulated receptors were affected by CO2; 4 were stimulated and 8 inhibited. Receptors inhibited by CO2 were also inhibited by negative pressure while receptors stimulated by CO2 were also stimulated by negative pressure. These results show that CO2-responsive laryngeal receptors are not specialized endings. Although it is not clear to what extent each separate group of laryngeal receptors is involved, each may contribute to the reflex bradypnea which has been observed during exposure of the upper airway to elevated levels of CO2. However, the importance of CO2-responsive laryngeal receptors in physiological conditions remains unclear.

Animals↗
PubMed1990

Water-responsive laryngeal receptors in the dog are not specialized endings.

The primary purpose of this study was to ascertain whether laryngeal receptors activated by water are specialized endings or whether they also respond to other stimuli, such as pressure, temperature and laryngeal motion as they occur during the breathing cycle. In 35 anesthetized mongrel dogs, breathing spontaneously through a lower cervical tracheostomy, water and other test solutions at approximately 37 degrees C were injected into the functionally isolated larynx with a small catheter. Of the 130 receptors studied, none of the cold receptors (N = 13) responded to water, whereas approximately 60% of all laryngeal mechanoreceptors (72 of 117) responded with either a short delay, short duration or a long delay, long duration response. In general the former pattern of response was exhibited by nonrespiratory-modulated receptors, whereas the latter was typical of respiratory-modulated receptors. The specific nature of the stimulus (hypotonicity or lack of chloride ion) of the water response was further studied in 53 receptors with isoosmotic solutions of dextrose and sodium gluconate. The long delay, long duration response was dependent on a decreased osmolality, while the short delay, short duration response was dependent on the lack of chloride ion of the test solutions. All water-responsive receptors tested (N = 17) were blocked within 50 sec by topically applied 2% lidocaine and thus presumed to be superficial. However, 10 receptors which did not respond to water were also blocked within 50 sec, suggesting that not all superficial receptors are stimulated by water. Based on these observations, we propose that changes in osmolality or ionic composition of the laryngeal surface liquid could play an important role in modifying reflexes involved in the maintenance of upper airway patency.

Animals↗
PubMed1990

Cooling mediates the ventilatory depression associated with airflow through the larynx.

Although constant airflow through the upper airway has been shown to induce ventilatory depression in anesthetized newborn animals, the role of laryngeal temperature in this response has not been studied. Experiments were performed in fourteen 1-5 day-old anesthetized puppies breathing through a tracheostomy. Tidal volume and laryngeal temperature were recorded while a constant stream of air (15-25 ml/sec) at room temperature was passed in the expiratory direction for 20 sec through the isolated upper airway. Warm (35-37 degrees C), humidified air at the same flow served as control. When laryngeal temperature was decreased by 7.5 +/- 0.9 degrees C, a marked change in breathing pattern was observed (VT = 54 +/- 5, TI = 187 +/- 33, TE = 636 +/- 179, VT/TI = 45 +/- 10% of control; n = 9). Warm air at the same flow induced no significant changes. Superior laryngeal nerve section abolished the effects of cooling on breathing pattern. In 5 puppies we compared the effect of 'fast' and 'slow' laryngeal cooling. Fast trials altered breathing pattern earlier than slow trials. We conclude that the depressant effect of airflow through the upper airway is entirely due to a decrease in laryngeal temperature and is mediated by superior laryngeal nerve afferents.

Animals↗
PubMed1989

Sucking and breathing patterns during breast- and bottle-feeding in term neonates. Effects of nutrient delivery and composition.

We attempted to determine whether differences in milk composition or flow rate are the primary determinants in altering breathing pattern during nipple-feeding. In the first phase of the study, 15 neonates were studied during breast-feeding and bottle-feeding; in the second phase, 15 were evaluated during bottle-feeding of expressed human milk and formula. A reduction in inspiratory duration was observed with all feeding regimens. Moreover, significant prolongation in expiratory duration and reduction in breathing frequency were observed during bottle-feeding of formula and expressed human milk (compared with control); these effects were greater with formula feeding. Higher sucking frequency was observed during breast-feeding compared with bottle-feeding; no difference in suckling frequency or sucking pressure was observed between bottle-feeding of expressed human milk and formula. We conclude that most of the differences in sucking and breathing patterns between breast- and bottle-feeding can be attributed to nutrient delivery rather than nutrient composition.

Bottle Feeding↗
PubMed1989

Specificity of esophageal electrode recordings of posterior cricoarytenoid muscle activity.

Esophageal electrodes have been used for recording the electromyographic (EMG) activity of the posterior cricoarytenoid muscle (PCA). To determine the specificity of this EMG technique, esophageal electrode recordings were compared with intramuscular recordings in eight anesthetized mongrel dogs. Intramuscular wire electrodes were placed in the right and left PCA, and the esophageal electrode was introduced through the nose or mouth and advanced into the upper esophagus. On direct visualization of the upper airway, the unshielded catheter electrode entered the esophagus on the right or left side. Cold block of the recurrent laryngeal nerve (RLN) ipsilateral to the esophageal electrode was associated with a marked decrease in recorded activity, whereas cold block of the contralateral RLN resulted only in a small reduction in activity. After supplemental doses of anesthesia were administered, bilateral RLN cold block essentially abolished the activity recorded with the intramuscular electrodes as well as that recorded with the esophageal electrode. Before supplemental doses of anesthesia were given, especially after vagotomy, the esophageal electrode, and in some cases the intramuscular electrodes, recorded phasic inspiratory activity not originating from the PCA. Therefore, one should be cautious in interpreting the activity recorded from esophageal electrodes as originating from the PCA, especially in conditions associated with increased respiratory efforts.

Animals↗
PubMed1989

Time of application of negative pressure pulses and upper airway muscle activity.

Effect of upper airway pressure changes on thoracic inspiratory muscles has been shown to depend on the time of application during the breathing cycle. The present study was designed to investigate the importance of the time of application of upper airway negative pressure pulses on upper airway muscles. The upper airway was functionally isolated into a closed system in 24 anesthetized spontaneously breathing rabbits. Negative pressure pulses were applied in early (within the first 200 ms) and late (greater than or equal to 200 ms) inspiration, while electromyograms (EMG) of the diaphragm (Dia), genioglossus (GG), alae nasi (AN), and/or posterior cricoarytenoid (PCA) muscles were simultaneously monitored. When negative pressure pulse was applied in early inspiration, the increase in GG activity was greater [0.49 +/- 0.37 to 4.24 +/- 3.71 arbitrary units (AU)] than when negative pressure was applied in late inspiration (0.44 +/- 0.29 to 2.64 +/- 3.05 AU). Similarly, increased activation of AN (2.63 +/- 1.01 to 4.26 +/- 1.69 AU) and PCA (3.46 +/- 1.16 to 6.18 +/- 2.93 AU) was also observed with early inspiratory application of negative pressure pulses; minimal effects were seen in these muscles with late application. An inhibitory effect on respiratory timing consisting of a prolongation in inspiration (TI) and a decrease in peak Dia EMG/TI was observed as previously reported. These results indicate that the time of application of negative pressure during the breathing cycle is an important variable in determining the magnitude of the response of upper airway muscles.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Reflex responses to capsaicin: intravenous, aerosol, and intratracheal administration.

Intravenous capsaicin elicits the "pulmonary chemoreflex" (apnea, bradycardia, and hypotension) presumably through the stimulation of "pulmonary C-fibers." The present study was designed to ascertain whether tracheobronchial C-fibers play a role in the above reflex response. We compared the effects of capsaicin injected intravenously, administered as an aerosol, and administered topically into the intrathoracic trachea in anesthetized dogs (n = 17) and rats (n = 17). We measured esophageal, subglottic, and arterial pressures together with abdominal muscle electromyogram. Changes in expiratory duration [(TE), measured as the ratio TEtest to TEcontrol, mean +/- SD] due to capsaicin were similar with all three routes of administration in both dogs (intravenous, 7.9 +/- 4.6; aerosol, 5.5 +/- 3.1; topically into intrathoracic trachea, 7.1 +/- 4.8) and rats (intravenous, 22.6 +/- 10.3; aerosol, 11.1 +/- 8.2; topically into intrathoracic trachea, 21.6 +/- 4.6). An increase in laryngeal resistance was a constant finding in the rat, but it was less frequent in the dog. Cardiovascular responses consisting of bradycardia and hypotension occurred with all three routes of administration but had longer delays than the respiratory responses. Capsaicin instillation into the extrathoracic trachea in dogs (n = 7) also induced qualitatively similar cardiorespiratory responses. We conclude that 1) capsaicin-sensitive receptors are accessible from both the pulmonary circulation and the airway lumen and 2) afferents, even in the extrapulmonary portion of the tracheobronchial tree, can play a role in the reflex responses to intraluminal capsaicin.

Administration, Inhalation↗
PubMed1988

Relative contribution of ribcage and abdomen during augmented breaths in infants.

Changes in the relative contribution of ribcage and abdomen during augmented breaths were assessed in two groups of infants (less than 2 weeks and 4-12 weeks old). In both groups ribcage and abdominal movements increased during augmented breaths in quiet sleep. In the older infants the relative increase was greater for the ribcage (P less than 0.05) when expressed either as a ribcage to abdominal movement ratio or as a percent of the respective movements during control breaths. In contrast, no significant change of the relative contribution was observed in the younger age group. During active sleep paradoxical movement of the ribcage, observed during tidal breaths, continued during the first phase of the augmented breath; however, during the second phase of inspiration, the ribcage moved outward in all but one infant. Our results show that marked increases in tidal volume are associated with greater increases in ribcage contribution in infants beyond the neonatal period. This may reflect differences in recruitment patterns of intercostal muscles during development.

Abdominal Muscles↗
PubMed1988

Respiratory control during nipple feeding in preterm infants.

The present study was designed to investigate the development of respiratory control during feeding in premature infants. Cardiorespiratory disturbances during feeding were evaluated with polygraphic monitoring in 24 premature infants within 1 week of beginning nipple feeds. During the initial study, 15 infants exhibited one or more episodes of short apnea (greater than or equal to 10 sec) and three infants exhibited prolonged apnea (greater than or equal to 20 sec). Bradycardia developed in seven infants; apnea and decreases in oxygen saturation invariably preceded the development of bradycardia. In contrast, short apnea occurred during sleep in five infants and associated bradycardia developed in four infants. Occurrence of apnea during sleep was significantly lower than that observed during feeding (P less than 0.05). Subsequently, 18 of these infants were reevaluated 7-10 days later. Seven infants developed one or more episodes of short apnea, five developed prolonged apnea, and four developed bradycardia. These occurrences were not significantly different from those observed during the initial study (P greater than 0.05). Short apnea persisted during sleep in four infants during reevaluation. Most of the apneic episodes in both studies were mixed apnea. The high frequency of cardiorespiratory disturbances during the first 2 weeks of nipple feeding indicates that in most preterm infants respiratory control during feeding is still immature at the postconceptional age of 35-36 weeks.

Apnea↗
PubMed1988

Characteristics of laryngeal cold receptors.

This study was designed to further characterize the properties of previously described laryngeal cold receptors (Respir. Physiol. 59:35, 1985). Single unit action potentials were recorded from the internal branch of the superior laryngeal nerve (SLN) in anesthetized, spontaneously breathing dogs. The nervous conduction of fibers originating from 12 laryngeal cold receptors was blocked at a mean (+/- SE) temperature of 18.8 +/- 0.7 degrees C. Twelve receptors were localized on the edge of the vocal folds in correspondence of the vocal process of the arytenoid cartilage. Topical anesthesia (2% lidocaine) blocked their activity within 4-18 sec, suggesting a superficial location. Paralysis of the vocal folds during spontaneous breathing through the upper airway did not alter the activity of 9 of 13 cold receptors. On the other hand, 7 of 12 cold receptors tested with constant flow showed respiratory modulation and laryngeal paralysis abolished the modulation of 3 of these tested with a constant flow of air. During progressive cooling in a stepwise fashion, as in frigid air breathing, laryngeal cold receptors maintained a phasic discharge. Our results indicate that these endings are particularly suited for detecting changes in temperature.

Animals↗
PubMed1988

Contraction of trachealis muscle and activity of tracheal stretch receptors.

This study examined the relationship between tracheal slowly adapting stretch receptor discharge and smooth muscle activity in a preparation in which the efferent supply to the airway was essentially intact. In 7 anesthetized, paralyzed, artificially ventilated dogs, smooth muscle activity was assessed by measuring the pressure of a water-filled cuff placed in the extrathoracic trachea and action potentials originating from 19 extrathoracic tracheal stretch receptors were recorded from the superior laryngeal nerve. Challenges were: hypercapnia (FI = 0.05 and FI = 0.10), hypoxia (FI = 0.10 and FI = 0.05) and asphyxia. Concurrent increases in cuff pressure and receptor discharge were present in 18 of the endings studied in response to all the challenges presented. The remaining receptor increased its rate of discharge with 10% CO2 and asphyxia; neither receptor discharge or cuff pressure increased with 5% CO2 and hypoxia. Following block of the recurrent laryngeal nerves, baseline values of both cuff pressure and receptor discharge, as well as the responses to asphyxia, decreased; any residual response was eliminated by atropine. Of the 17 receptors whose location could be precisely ascertained, 14 were found in the proximal third of the extrathoracic trachea, and the remaining 3 in the middle third. The temperature at which the nervous conduction was blocked was determined for 3 slowly adapting receptors; it ranged from 4.5 to 12.5 degrees C. Of 5 extrathoracic tracheal rapidly adapting receptors encountered during the course of the experiments, 3 were tested with asphyxia and found to be unaffected. This study shows that tracheal slowly adapting stretch receptors are activated by smooth muscle contractions reflexly induced by chemoreceptor stimulation.

Animals↗
PubMed1988

Laryngeal paralysis on receptor and reflex responses to negative pressure in the upper airway.

Mechanoreceptors affected by changes in transmural pressure and/or contraction of intrinsic muscles are present in the larynx. This study is designed to test the hypothesis that laryngeal paralysis alters laryngeal mechanoreceptor and reflex responses to collapsing pressure. Experiments were carried out on anesthetized, spontaneously breathing dogs. The activity of 65 mechanoreceptors was recorded from the superior laryngeal nerve during upper airway occlusion before and during laryngeal paralysis induced by cold block of both recurrent laryngeal nerves (RLN). Esophageal and upper airway pressures were also recorded. Thirty-three laryngeal mechanoreceptors stimulated by negative pressure decreased their inspiratory activity during upper airway occlusion from 48.1 to 30.4 imp/sec when the RLNs were blocked. In contrast, 21 inspiratory modulated mechanoreceptors inhibited by negative pressure and 11 responding only to negative pressure did not change their activity during RLN block. The effect of laryngeal paralysis on the cricothyroid muscle response to negative pressure was assessed in 7 dogs and found to be minimal. These results suggest that 'drive' receptors stimulated by negative pressure do not play a significant role in the reflex activation of upper airway dilating muscles.

Animals↗
PubMed1988

Interaction between upper airway negative pressure pulses and CO2 on breathing pattern.

The interaction between CO2 and negative pressure pulses on breathing pattern was investigated in 10 anesthetized, spontaneously breathing rabbits. The upper airway was functionally isolated into a closed system. A servo-respirator triggered by the inspiratory activity of the diaphragm was used to apply pressure pulses of -15 cmH2O to the isolated upper airway in early inspiration while the animal was breathing room air, 100% O2, 6% CO2 in O2, or 9% CO2 in O2. The negative pressure pulses produced a reversible inhibition of inspiration in most trials with resultant increase in inspiratory duration (TI); no change was observed in peak diaphragmatic electromyogram (Dia EMG) or expiratory duration, whereas a decrease was seen in mean inspiratory drive (peak Dia EMG/TI). This prolongation of inspiratory duration and decrease in mean inspiratory drive with negative pressure pulses persisted at higher levels of CO2; the slopes of the test breaths were not significantly different from that of control breaths. These results suggest that upper airway negative pressure pulses are equally effective in altering the breathing pattern at all levels of CO2.

Animals↗
PubMed1988

Nipple units for newborn infants: a functional comparison.

Milk flow characteristics of nipple units commonly used in the neonatal period were compared in the laboratory using a mechanical system. The number of simulated sucks required to empty 120 mL of formula was determined for each nipple unit. In general, the number of simulated sucks required to empty the bottle decreased when the applied negative pressure was increased from -60 to -120 cm of H2O except for SMA nipple units for premature infants. The Nuk type required less sucks (ie, higher flow) than standard nipple units. Among the Nuk-type nipple units, the SMA nipple had the highest mean flow and Enfamil Natural the lowest mean flow; among the standard nipple units, SMA single-hole had the highest flow and Ross Twist-on had the lowest flow. However, wide variability in performance was observed not only between different types of nipple units but also within the same type. Flow characteristics of nipple units for preterm infants overlapped markedly, with that for term neonates with Enfamil nipples exhibiting the highest flow. Clinical relevance of these differences in flow characteristics among the nipple units is discussed.

Bottle Feeding↗
PubMed1987

Respiratory activity in the superior laryngeal nerve of the rabbit.

We studied the respiratory modulation of laryngeal afferents and their response to transmural pressure in 24 anesthetized, spontaneously breathing rabbits. Laryngeal afferent activity has a predominant inspiratory augmentation during tracheal breathing or tracheal occlusion that can be accounted for by the respiratory movement transmitted to the larynx through the trachea. During upper airway breathing or upper airway occlusion SLN afferent activity increases in expiration and decreases in inspiration. This respiratory modulation is due to changes in upper airway pressure (Pua). In fact, positive pressure stimulates SLN afferent activity, while negative pressure inhibits it. Mechanical restriction of epiglottal movement reduced the response to Pua changes during upper airway occlusion and application of maintained positive (0.1-0.5 kPa) and negative (-0.1 to -0.5 kPa) pressures (P less than 0.005). Furthermore, surgical removal of epiglottis decreased the baseline activity of SLN to 16.5% of control. These experiments suggest that in the rabbit the epiglottis is the main source of SLN afferent activity and that its displacement, due to changes in Pua, is the most important factor for modulating SLN activity. Most of the laryngeal receptors showed an inspiratory augmentation with tracheal breathing and occlusion, were stimulated by positive pressure and inhibited by negative pressure, reflecting the behavior observed in the whole nerve.

Animals↗