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Biomedical subjects

O P Mathew

Publications and source records attributed to O P Mathew.

At least 19 recordsLinked to original sources
PubMed1992

Sucking patterns of neonates during bottle feeding: comparison of different nipple units.

The present study was designed to compare the sucking pattern of term and preterm infants during bottle feeding with different types of nipple units (Enfamil single-hole nipple units for term and preterm infants and SMA Nuk nipple units). In addition, the sucking pattern of term neonates during a feeding regimen commonly used in many feeding studies was evaluated (reservoir nipple system). In this system milk flows from a reservoir through a tube and depends on the sucking pressure generated by the infant. Only the Enfamil single-hole nipple units for term and preterm infants were compared in preterm infants. No significant difference in sucking frequency was observed in term neonates with different types of nipple units. Although the mean sucking pressures generated tended to be less among nipple units with higher flow, these differences were not statistically significant. Similarly, no significant difference in total sucking or feeding time was observed among the three nipple units tested. Sucking pressures generated by term infants were significantly less when milk flow was increased markedly utilizing the reservoir system. In preterm infants no differences in sucking frequency, sucking pressure, mean flow, or total feeding time were observed when sucking patterns with term and preterm nipple units were compared. Implications of these findings in feeding neonates are discussed.

Bottle Feeding↗
PubMed1992

Response of laryngeal mechanoreceptors to high-frequency pressure oscillation.

High-frequency pressure oscillations (HFPO) in the upper airway induce arousal, activation of genioglossus muscle, and bronchoconstriction. The present study was designed to determine the response of superior laryngeal nerve afferent fibers to HFPO. In 10 anesthetized dogs spontaneously breathing through a tracheal cannula, the upper airway was converted to a closed system. The activity of thin bundles separated from the peripheral cut end of the superior laryngeal nerve was monitored. Of 104 mechanoreceptors identified, 87 were classified as respiratory modulated and 17 as non-respiratory modulated on the basis of their response to transmural pressure change and muscle activity. The responses of these fibers to HFPO of +/- 2.5 cmH2O at 10, 20, and 30 Hz were determined. Among the respiratory-modulated receptors, 86 of 87 increased their activity in response to HFPO. Of the 17 non-respiratory-modulated receptors, 12 receptors showing a random or tonic activity did not respond to HFPO, whereas the 5 that were silent during control condition responded exclusively to HFPO. Our results show that HFPO of similar frequency but much less magnitude than snoring is capable of activating the vast majority of laryngeal mechanoreceptors. Pressure-sensitive respiratory-modulated endings appear to mediate the arousal and genioglossal response, whereas non-respiratory-modulated receptors responding to HFPO presumably mediate the bronchoconstrictive response.

Air Pressure↗
PubMed1992

Decrease in lung volume-related feedback enhances laryngeal reflexes to negative pressure.

Negative pressure applied to the upper airway has an excitatory effect on the activity of upper airway muscles and an inhibitory effect on thoracic inspiratory muscles. The role of lung volume feedback in this response was investigated in 10 anesthetized spontaneously breathing adult rabbits. To alter lung volume feedback, the lower airway was exposed to SO2 (250 ppm for 15 min), thereby blocking slowly adapting receptors (SARs). Negative pressure pulses (5, 10, and 20 cmH2O, 300-ms duration) were applied to the functionally isolated upper airway before and after SAR blockade. Tracheal airflow and electromyogram (EMG) of the genioglossus and alae nasi were recorded. Peak EMG, peak inspiratory flow, tidal volume, and respiratory timing of control breaths (3 breaths immediately preceding test) and test breaths were determined. Analysis of variance was used to determine the significance of the effects. Negative pressure pulses increased peak EMG of genioglossus and alae nasi and inspiratory duration and decreased peak inspiratory flow. These effects were larger after SAR blockade. We conclude that a decrease in volume feedback from the lung augments the response to upper airway pressure change.

Animals↗
PubMed1991

Breathing patterns of preterm infants during bottle feeding: role of milk flow.

Milk flow achieved during feeding may contribute to the ventilatory depression observed during nipple feeding. One of the important determinants of milk flow is the size of the feeding hole. In the first phase of the study, investigators compared the breathing patterns of 10 preterm infants during bottle feeding with two types of commercially available (Enfamil) single-hole nipples: one type designed for term infants and the other for preterm infants. Reductions in ventilation, tidal volume, and breathing frequency, compared with prefeeding control values, were observed with both nipple types during continuous and intermittent sucking phases; no significant differences were observed for any of the variables. Unlike the commercially available, mechanically drilled nipples, laser-cut nipple units showed a markedly lower coefficient of variation in milk flow. In the second phase of the study, two sizes of laser-cut nipple units, low and high flow, were used to feed nine preterm infants. Significantly lower sucking pressures were observed with high-flow nipples as compared with low-flow nipples. Decreases in minute ventilation and breathing frequency were also significantly greater with high-flow nipples. These results suggest that milk flow contributes to the observed reduction in ventilation during nipple feeding and that preterm infants have limited ability to self-regulate milk flow.

Bottle Feeding↗
PubMed1991

Response of laryngeal receptors to water solutions of different osmolality and ionic composition.

Water-responsive laryngeal receptors with fibres in the superior laryngeal nerve were studied to characterize the specific physicochemical properties of aqueous solutions that activate these endings. The responses to water (37 degrees C) of 141 receptors were studied in 39 anaesthetized dogs breathing through a tracheostomy with the larynx functionally isolated. Of the 89 receptors stimulated by water, 53 were also challenged with isosmotic (275-315 mOsm) solutions of dextrose and sodium gluconate at 37 degrees C. Receptors that only responded to water (n = 31) with a long delay, long duration discharge were generally respiratory modulated. On the other hand, laryngeal receptors that responded to all test solutions (n = 22) with a short delay, short duration discharge were generally not respiratory modulated. We conclude that the former type of receptor responds to lower osmolality, whereas the latter responds to the lack of chloride ions in the test solutions. These two types of receptor may be responsible for the cough and bronchoconstriction induced by inhaled aerosols of different osmolalities and ionic compositions.

Action Potentials↗
PubMed1991

Behavioral arousal in newborn infants and its association with termination of apnea.

Arousal is an important protective mechanism that aids in the resolution of obstructive sleep apnea in adults and children, but its role in neonatal apnea has not been investigated. The primary aim of the present study was to determine the role of arousal in the termination of apnea in preterm infants. Videorecording was used to identify spontaneous behavioral arousal in a group of healthy full-term (n = 7) and preterm (n = 10) infants before and during polygraphic monitoring of cardiorespiratory variables and in a group of preterm infants with apnea (n = 10) during similar polygraphic monitoring. Spontaneous arousal rates (mean +/- SE) in full-term infants before and during polygraphic monitoring were 0.18 +/- 0.03 and 0.23 +/- 0.07 episodes/min, respectively. Corresponding values in nonapneic preterm infants were 0.24 +/- 0.03 and 0.24 +/- 0.02 episodes/min. In apneic preterm infants, mean spontaneous arousal rate during polygraphic recording was 0.26 +/- 0.02, but it was considerably higher during apneic sleep periods (0.59 +/- 0.17) than during nonapneic sleep periods (0.25 +/- 0.01). The frequency of occurrence of arousal was significantly higher (P less than 0.005) in long vs. short apnea, mixed vs. central apnea, and severe vs. mild apnea. Although a clear association between arousal and apneic resolution was observed in preterm infants, lack of arousal responses in a large number of apneic episodes suggests that behavioral arousal is not essential for the termination of apnea in these infants.

Airway Obstruction↗
PubMed1991

Motor activity and apnea in preterm infants. Is there a causal relationship?

It is generally believed that all apneic episodes in preterm infants occur during sleep. Because occurrence of apnea during wakefulness has been documented in these infants, we investigated its frequency and characteristics in 10 premature infants using simultaneous polygraphic and video recordings. Behavioral arousal with motor activity preceded the onset of apnea in 202 episodes. Approximately 60% of episodes began within 15 s of arousal. Whereas most of the episodes were short and asymptomatic, hypoxia and/or bradycardia developed during 18 apneic spells, and these episodes accounted for a third of all apneic episodes that resulted in bradycardia or hypoxia in these infants studied. Essentially, all movement-related apneas (17 of 18) began within 15 s of arousal; motor activity continued throughout apnea in 13, whereas apnea resolved after cessation of motor activity in the remaining five. The main finding of the present study is that movement-related apnea is far more frequent than previously recognized. This finding is important in the clinical management of preterm infants with apnea.

Apnea↗
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↗
PubMed1978

Effect of digoxin and diuretics on high altitude left ventricular dysfunction.

Systolic time intervals, stroke volume, cardiac output and (dZ/dt)/RZ index were serially estimated in 51 normal healthy volunteers at sea level, for ten days after air induction to 3658 m altitude and on return to sea level. The subjects were divided into three groups and were administered a diuretic, beta methyldigoxin and placebo in a double blind protocol. The group on placebo showed an increase in heart rate, reduction in stroke index and cardiac index during high altitude exposure with normalization on return to sea level. A deterioration in left ventricular function as manifested by prolongation of pre-ejection period, increase in PEP/LVET ratio, reduction in (dZ/dt)/RZ index and left ventricular ejection time was also noted at high altitude. The subjects on digoxin maintained normal stroke/cardiac index and did not show any significant changes in the parameters of myocardial function. The diuretic group showed more deterioration in the parameters than the placebo group. No significant side effects were noted. Left ventricular dysfunction and reduction of stroke index at high altitudes may be causually related; digoxin administration may prevent them from occurring.

Adult↗