Charles H. Hendricks

Cardiac output during labor

Abstract 1. 1. In a study of 47 patients by a modified pulse pressure method, changes in cardiac output were recorded during late pregnancy, in labor, and in the early puerperium. This is the first report on cardiac output in labor. 2. 2. During effective contractions in labor, the cardiac output rises an average of 30.9 per cent over the output in the resting state. 3. 3. The act of bearing down in the absence of a contraction results in most cases in a small but transient drop in cardiac output. Bearing down with a contraction, however, may result in an actual increase in output. 4. 4. Pain and anxiety can produce significant elevations in cardiac output. 5. 5. Placental separation per se was not demonstrated to result in consistent variations in cardiac output. Contraction of the uterus post partum, however, may raise the output level significantly. 6. 6. Cardiac output appears to rise during the first stage of labor, and may rise even further at delivery. In some cases a small additional rise is seen in the first few minutes post partum. The output persists at a moderately elevated level for a variable period thereafter.

The hemodynamics of a uterine contraction

Abstract 1. 1. An attempt has been made to estimate by indirect methods the amount of blood extruded from the uterus into the maternal venous reservoir during the early portion of the contraction cycle. From this study it would appear that this volume of blood may be in the range of 250 to 300 c.c. 2. 2. The blood pressure rises quite consistently during a uterine contraction. Most commonly, the systolic pressure rises by 10 to 20 mm. Hg, while the rise in diastolic pressure is somewhat less. 3. 3. During the early part of the contraction the heart rate tends to rise, followed by a substantial lowering of the rate by the time the contraction is at its maximum intensity. 4. 4. The stroke volume appears to drop slightly during the initial stages of the contraction cycle, after which it rises significantly above the base line level. 5. 5. The heart rate and stroke appear to maintain a somewhat reciprocal relationship throughout the contraction cycle. 6. 6. Central venous pressure rises in response to a uterine contraction. Brachial venous pressure shows little or no response. Femoral venous pressure rises sharply in the very earliest phase of the contraction, and then drops to a somewhat lower elevation for the rest of the active portion of the contraction, after which it subsides to its original level.

Inherent motility patterns and response characteristics of the nonpregnant human uterus

WIT H IN A FEW YEAR s after Schatz’ published his epochal studies of human uterine activity in pregnancy as recorded through an intrauterine estraovular bag, Heinricius” proposed a modification of the method to permit recording of activity of the nonpregnant uterus in viva through the use of a thin rubber bag. In this country, the first published record of uterine activity was by Iiucker.” The work of Knaus,“, .‘, starting in 1929. marked the beginning of a tremendous expansion of this field of study. Knaus’ original work, on which he based his primary findings conccrninz uterine activity at the various phases of the cycle and the response to pituitrin, was carried out by the injection of radiocontrast medium into the uterus through a metal cannula fitted with a rubber retaining tip, according to the standard method for hysterosalpinLyography. He then recorded changes in intrauterine prcssure through the end of the metal catheter. By 1933 he had changed to the balloon recordinz technique. A complete re\Gw of methods previously

Uterine contractility at delivery and in the puerperium

Abstract 1. 1. Uterine activity has been recorded continuously throughout labor, delivery, and into the puerperium by recording pressure alterations transmitted through open-end fluid-filled catheters placed either within the uterine cavity or deep within the myometrium. 2. 2. The initially high uterine activity present immediately after delivery of the baby diminishes smoothly and progressively during the first 1½ to 2 hours post partum, after which it eventually becomes quite stable. A fairly steady diminution in the frequency of contractions is observed regularly. The diminution in the intensity of contractions is less predictable. 3. 3. The high intensity of the contractions post partum (often more than 300 mm. Hg and occasionally up to 400 mm. Hg) is presumed to be due to the greatly diminished volume about which the still active uterus contracts. 4. 4. Distinctive and nearly identical patterns of incoordination may be observed in the same patient in late prelabor and at some time in the puerperium. 5. 5. The incoordinate contractions which begin to appear several hours post partum, and which tend to become increasingly incoordinate with the passage of more time can be partially or wholly restored to coordination either by the administration of oxytocin in proper dosage or by the application of an oxytocin-releasing stimulus (suckling). 6. 6. The relationship between the appearance of incoordinate uterine activity (both ante partum and post partum) and the demonstrated effect of oxytocin in producing coordination (both ante partum and post partum) appears to offer further support to the concept that oxytocin plays an active part in normal human parturition. 7. 7. With further knowledge of the physiology of puerperal uterine activity as compared with that before delivery, the method employed in this study should be helpful in the preliminary assaying of various pharmacologic agents which appear to hold some promise of usefulness in the antepartal state.

Pressure relationships between the intervillous space and the amniotic fluid in human term pregnancy

Abstract 1. 1. The intervillous space and the amniotic fluid pressures were recorded simultaneously and continuously for prolonged periods of time. 2. 2. As long as the uterus is not in active systole, the pressures in the two spaces remain virtually identical. 3. 3. Recording on a sensitive scale the pressure difference between the intervillous space and the amniotic fluid shows that during uterine systole the amniotic fluid pressure increases slightly faster than does the pressure in the intervillous space, the average maximum differential being approximately 2.6 mm. Hg. This pressure differential is partially “erased” by virtue of the fact that the pressure in the intervillous space makes up part of the pressure deficit by the time the apex of the contraction is reached. 4. 4. Movement of the patient brings about alterations in the pressure of approximately equal amounts in both spaces, and without appreciable lag. The amniotic fluid-intervillous space pressure relationship seems to be unaffected by either rupture of the membranes or the administration of oxytocin in physiologic dosage.

Cerebrospinal fluid pressure in labor

Abstract 1. 1. The CSFP elevation in response to a uterine contraction is predictable and consistent. It is associated with an increase in central venous pressure, ABP, stroke volume, and cardiac output. 2. 2. The maternal circulatory system serves as “transducer” which readily transmits the pressure change to the CSFP even in the presence of sleep and total sensory blockade. 3. 3. Respiratory cycle changes in CSFP demonstrate the rapidity with which changes in intrathoracic venous pressure can be communicated to the central nervous system. The Valsalva maneuver produces an exaggerated respiratory response. 4. 4. This study does not support the theory that the injection of a spinal anesthetic should be delayed during a uterine contraction because of turbulence of the cerebrospinal fluid.

Effect of medroxyprogesterone acetate upon the duration and characteristics of human gestation and labor

The effect of medroxyprogesterone acetate upon the duration and char acteristics of human gestation and labor was studied. 200 pregnant women (36-38 weeks gestation) were randomly assigned to a group receiving 20 mg 4 times/day or to a group receiving only the tablet base. This double-blind study failed to reveal any effect upon the duration of pregnancy or the characteristics of pregnancy labor or fetal conditions.

Delivery patterns and reproductive efficiency among groups of differing socioeconomic status and ethnic origins

Abstract In order to assess the relative importance of ethnic versus socioeconomic components as they affect reproductive performance two groups of women, one white and one nonwhite, were studied. The socioeconomically more favored (private service patients) were compared with the socioeconomically less favored (staff service) in each group. It was found that the groups of higher socioeconomic standing resemble each other in their obstetric performance more than they resemble their ethnic counterparts in the less-favored groups. Both of the higher socioeconomic groups exhibited superior reproductive performance in the following parameters: perinatal mortality, prematurity by weight, prematurity by weeks, ectopic pregnancy, and pre-eclampsia.

Use of intranasal oxytocin in obstetrics

Abstract 1. 1. With use of intrauterine catheters to record uterine activity, the effect of intranasal administration of synthetic oxytocin was studied in a series of 23 pregnant subjects, 16 of whom were at or beyond term, the remainder begin at 38, 36, 34, 30, 28, 22, and 12 weeks, respectively. 2. 2. The drug was applied either in drops or in the form of a fine spray from a small plastic squeeze bottle. 3. 3. Following administration of the drug, any increase in uterine activity usually appears within 5 to 7 minutes. 4. 4. The peak activity is usually achieved within 10 to 20 minutes, after which there usually begins a slow decline toward the level of spontaneous activity. 5. 5. A single instantaneous intranasal application of the drug represents a very modest dose, the effect being roughly comparable to that brought about by the continous intravenous infusion of 2 mU of oxytocin per minute for 5 minutes. 6. 6. The contractions stimulated by oxytocin are indistinguishable in all characteristics from spontaneously occurring contractions. 7. 7. The amount of response induced by intranasal oxytocin is principally dependent upon the degree of sensitivity to oxytocin which the uterus has previously achieved.

Patterns of increasing uterine activity in late pregnancy and the development of uterine responsiveness to oxytocin

Abstract 1.1. The development of spontaneous uterine activity and oxytocin response patterns was studied by the performance of 641 intranasal oxytocin tests on 348 women in late pregnancy. 2.2. Spontaneous uterine activity increases progressively during the last 6 weeks of pregnancy, reaching its maximum in the week before labor. 3.3. Response to oxytocin follows a pattern parallel to that of spontaneous uterine activity, also reaching its maximum in the final week before the onset of spontaneous labor. 4.4. The variability of the demonstrated responses from one individual to another was so great that it throws doubt upon the ability of any oxytocin sensitivity test which has yet been devised to predict accurately the onset of spontaneous labor in the individual patient.