Human Milk: Composition, Clinical Benefits and Future Opportunities. Группа авторов

shift between movements in each of these three areas. Ultrasound recordings from 29 mother/baby pairs (46 complete breastfeeds) were analyzed, although analysis was restricted to those periods when active sucking was taking place. Nonetheless, over 1 million frames of active sucking were analyzed in real-time by this technique.

      If movement occurred in sector 1 first, a negative phase shift was recorded relative to sector 2; a zero phase shift indicated an absence of a phase shift between sectors 1 and 2; while a positive phase shift indicated movement in sector 2 preceded that in sector 1. In practice, this was caused by the movement in sector 2 being of larger amplitude than that in sector 1 and was commonly evidence for the presence of an ETD being inserted (i.e., an “added” suction element being superimposed on a peristaltic wave).

Figure 4 encompasses approximately 70 sucks, and illustrates the transition from a period of almost pure “peristaltic” sucking (frames 0–1,000), to a “vacuum” phase where ETDs predominate (alongside PTMs) (frames 1,000–1,500).

Fig. 4. Section of analysis over a time frame of 60 s, embracing 70 sucks, which captures the transition from one style of suckling to another.

Table 1. Automated analysis of ultrasound recordings, exploring the phase shift in movement between the anterior and mid-sections of the oral cavity

The “movement detection rectangles” were manually drawn, so needed to be redrawn when there was movement artefact. Despite this limitation, the signal processing approach was applied to all 46 breastfeeding episodes, totaling 16 h of recording. Overall results of the analysis are shown in Table 1.¹

      PTMs were present throughout active sucking (100%), being: highly conspicuous for 78% of feeding, and predominating for over half of the time spent feeding, to the exclusion of ETDs (“suction/vacuum”). For a substantial period of feeding (27.5%), both PTMs and ETDS were equally visible, with no one method predominating over the other. For 22% of feeding, the added suction elements (ETDs) appeared to predominate. This analysis shows that ETDs [7, 12] were observable for roughly half of the time spent feeding.

Fig. 5. This figure shows the progression of a peristaltic wave from left (anterior) to right (posterior), across nine consecutive frames.

The same authors used a second analytical technique involving automated mapping of the contour of the surface of the tongue. This technique is capable of showing the progression, across successive frames, of a peristaltic wave from the anterior to posterior of the oral cavity. In Figure 5, the peristaltic wave is seen rising in amplitude, then declining, as it transitions (left to right) from the front to the back of the oral cavity.

One final piece of evidence supplied by this latter technique is that when an ETD is generated, the space created is generated as part of the standard peristaltic wave, as it progresses across the zone where the ETD appears; it is both opened at its leading edge initially, then closed off again from its anterior edge (Fig. 6).

      The two pictures show the contour of the dorsum of the tongue, which is automatically tracked (using the purpose-built software); the tongue outline is compressed left to right in this figure. The dotted line shows the tongue’s outline in the current frame, while the continuous line shows that in the previous frame. The circle circumscribes the mid-section of the baby’s tongue where the ETD is generated.

      The upper picture shows the precise moment the ETD starts to be generated, as the continuous line shows an absence of any indentation, while the dotted line peels away markedly to create an indentation (marked with an X), representing the start of the formation of an ETD “pocket.” In the lower picture, just four frames later, the ETD “pocket” is clear in the continuous line, and it is just starting to be closed off again, from the front (marked with a Y). This is the clearest evidence to date that added suction elements (ETDs) are created by the same core peristaltic process.

Fig. 6. This figure shows a localized added suck or extractive tongue depression, which is created from the front backwards. Four frames later, it is closed off again from the front backwards.

Returning to the most recent engineering-based study, Mortazavi et al. [21] created a complex model of the milk duct system of the breast, which they then combined with directly measured suction pressure data (Fig. 7) (from several babies), to define the parameter boundaries of the mathematical model. Modelled milk output was then compared with clinical data on milk transfer for a single baby.

Fig. 7. Phases of natural suckling (by 1 infant) transformed to a sequence of standardized sinusoidal waveforms (see inset). From Mortazavi et al. [21].

      No data were collected on positive stripping pressure, so axiomatically, any such element was excluded from the model, despite it being an explicit component of one of the key studies they cited [19]. Any theoretical model which only assumes that the baby behaves like a mechanical suction pump is likely either to verify that presumption [20], or find that it is inadequate to explain clinical data on milk transfer [21].

In order to use sucking data in their model as parameter boundaries, sucking profiles were transformed into single harmonic, sinusoidal waveforms, seemingly all with a periodic frequency approaching 1 Hz (1 suck/s) (Fig. 8). The need to simplify natural data for incorporation into their model was no doubt necessary, but this constrains the baby’s sucking pattern to even more closely resemble an electric breast pump.

      Their theoretical model simulated milk transfer by one baby, which was then compared with clinical data on intake by that baby. Based on this, the authors were forced to conclude that either sucking pressure alone, or total feed duration, did not account for: (a) the volume of milk removed, (b) the flow rate per unit time, or (c) the flow rate per suck.

This finding is unsurprising as it agrees with that of an earlier detailed study of the parameters of sucking pressure during breastfeeding [23], which was unable to find any association between suction and the 58% difference in intake between the first and second breast. Additionally, several authors have shown an inverse relationship between sucking pressure and milk flow during bottle-feeds: the greater the resistance to milk flow caused